Preventing Wi-Fi firmware updating

I know I can turn Wi-Fi off, but I like to get my new content from the Kobo store, and I want to have my Pocket articles synchronized -- but I *don't* want to have a new Firmware pushed to my device when I'm traveling, or before my favourite hacks (night mode, 2-finger brightness control for Aura) are updated. Is there a way I can do that? A config setting that says, "Don't update the firmware"? I would imagine that the Kobo support people must have some way of keeping units at older firmwares while otherwise accessing Wi-Fi, for testing purposes. Anybody know what the magic words are?

Thanks!