I've not been using FBReader for years, but my favorite piece of reading software AlReader (upon which the built-in Onyx OReader is based) has this feature for a long time now.
You can download the latest Alreader version that is specifically built to work with e-ink devices (and has specific integration with the T68) from here:
http://www.alreader.com/downloads/OT...ReaderEINK.apk
I know that I haven't answered the original question, but hope this helps.
Just note that all Onyx Android devices have non-standard APIs for some features (displaying the status bar, adjusting frontlight, refreshing the screen), so any reading app that you want to use needs to support Onyx specifically (it will not just work by default) or some of the functionality will not work. I'm not sure if FBReader has Onyx integration.