Just wanted to report that my attempt to swap internal memory was successful.
It was on a GLO, with a 8 GB card (Sandisk Ultra). I used the same tools that are mentioned on this thread (thanks!). I just finished copying ~2 GB of manga on it and all was recognised just fine.
I can't say I see any obvious speed improvement when using the device, but I've only had it for a day so it's hard to compare. It's certainly not slower. When using CrystalDiskMark on the USB-attached Glo (which is hardly the correct test) I get almost double the write speed and no change in read speeds.
If you can think of any relevant speed test I can make, I'm open to suggestions.
I'll reformat the original SD card so that I can benchmark it. This way, you'll at least be able to check if the card you're trying isn't slower.