I was poking around in libnickel.so.1.0.0 earlier, and I remembered a few users reporting that the patch "Block WiFi firmware upgrade" didn't actually work a few firmwares ago (as the patch description warns might be the case). I noticed the following strings appear near the "UpgradeCheck" strings that get patched:
Code:
https://api.ereaderupgrade.com
https://api.ereaderupgrades.com
https://api.kobobooks.com
Perhaps it would be possible to overwrite one or more of these strings to create a more reliable method of blocking firmware updates? Ideally it would be possible to block the firmware check without losing the ability to sync books and dictionaries, but I don't know which URLs Kobo uses for which functionalities.
As an easy test for an adventurous user, you could redirect these addresses to 127.0.0.1 in your Kobo hosts file, instead of editing libnickel.so.1.0.0 directly.