I think a data only cable can work. Power only cables do exist and are a good idea for unknown public sockets that might have malware, except then some gadgets that charge only take a lower current. The available current from a host is defined by existence or absence of two resistors on D- and D+ wires and if they go to +V or 0V. Higher current definitions are different for some makers, thus an iThing might only take full current from an Apple laptop or Apple compatible charger.
Also some chargers will confuse a Kobo ereader and make it "see" a PC host and it will offer to connect. Which is why you want a charge only cable before enabling the "USB Gadget mode" autoconnection without prompt in the configuration file. It should be possible to make a cable with the resistors compatible for your device on D- and D+ and then D+ and D- are not connected at "Host" end. Then you have to make sure and not use a USB power / charging socket with too low a current rating. PC host sockets are supposed to switch off if too much current is taken. You'd not want to assume a USB outlet built into a mains socket or that a USB charger does. Certainly most of the 12V Cigar socket adaptors just have a 5V IC regulator and the shut down or short current is whatever is designed into the IC. The D- and D+ lines may or may not have the resistors used by the gadget to sense what the maximum current is.
The host/charger NEVER sets charging current unless it's USB-C (which is so different it's not USB, it just can carry USB Data), it simply provides between 4.8 and 5.2V and the gadget decides what current to take. If more current is taken than the host socket/charger is designed for (like a short or a reversed V+ and 0V) it's supposed to turn off. This is a problem with USB-C as the maximum current is far higher than real USB and also it can do up to 5A and up to 20V. It ought to be 1A max at only 5V with shutdown if a short or reversed connection is detected in the absence of a command, but not all USB-C hosts/chargers implement it. A full power USB-C charger is much bulkier and much more expensive than a typical 1A 5V general purpose charger for USB.
USB has always struggled to keep up with the applications because originally it was only for joysticks, mouse, keyboard and small resolution cameras or small capacity memory (32 Mbyte = 0.032 G Byte was huge then). Stupidly it NEVER had peer to peer, so the extra pin was added on micro USB to tell the gadget to be a host instead of a slave, but then most gadgets can't charge in that state, though a few can with a special Y cable. A connector with up to 100W able to charge a laptop, or feed video and power to a display panel as well as do the USB serial data should have a new name. It's not USB which is purely a Host-Client serial data link with 5V only power. Even going more than 1A means lack of protection with faulty cables or gadgets. USB was 100mA, then 500mA. More than 1A was madness.
So anyway a power only cable is real, a power only cable that uses D+ and D- to indicate current that can be taken and only connects +V and OV at host/charger is real and a cable without +V and maybe even without 0V may work on some things.
Most cables sold as Charger cables are just ordinary USB cables. I've not found one that didn't connect D+ and D-, because then the gadget might only take 100mA or 500mA rather than 1A, 1.5A or 2A, with more than 1A or maybe 500mA needing a compatible charger / host as
not everyone uses the same arrangement of resistors.
The so-called enumeration or smart charging on less than USB-C is nothing of the sort. There is no communication. Just none, one or two resistors on the D+ and D- lines for the gadget to measure voltage on. USB-C uses a separate communication channel, Vbus, thus it's not actually a USB connection at all. Simply using "USB" as marketing.
Apple does not comply with USB (see
https://electronics.stackexchange.co...s-poweriq-work )
https://learn.adafruit.com/minty-boost/icharging
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(called enumeration) where it says "hey, I'm about to drag 500mA out of the computer, just so you know" and the computer can say "go ahead" or "no can do" (this is called the power negotiation).
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This is lie for children. The gadget simply measures the D- and D+ lines to deduce in SW or HW what current is available. There is no negotiation or signalling, except with USB-C.
This shows how silly it has got:
https://www.electronicdesign.com/tec...power-delivery
USB-C is so different to earlier USB standards it's only a marketing decision to call it USB.