IMO, all of the suggested solutions would really just be ugly hacks. Most importantly, they would be adversely affecting the overall usability of the device, whereas you really only want to affect the actual reader application.
I took a look at it, and the logic is hard-coded inside the reader application. From the 5.0.3 firmware (the last not-so-badly-obfuscated one):
Code:
if((float)a < 0.15F * (float)readerSDK.getUI().getReaderPane().getWidth())
doPrevPageAction();
else
doNextPageAction();
So the proper way would be to change that .15 value there to something suitable (and possibly the "<" to ">" if flipping is wanted).
JBPatch would be exactly the right tool for the job. Someone go ahead and write the patch so that it works on all supported firmwares, and I'll happily include it.
(This is probably a déjà-vu for many folks here, but anyway):
I would do it myself, if Lab126 weren't such dickheads. But because they are, JBPatch (and the patches) unfortunately have become a maintenance nightmare, and this is only going to get worse and worse with each new firmware release. So I'm not going to invest any more effort, because I know that every new firmware will mean even more (tedious, but boring) effort, only to adapt what was already working to their new obfuscation -- too much for one person.