couldn't the game like...detect if theres a plugins folder on the PSP, and if so, disabled online?
That could work....
(or somehow check the plugins loaded into the psp ram and if any are cfw, disable it..)

Also, if they catch a hacker, they should IP Ban, PSN Ban, MAC Ban, ect...
As with ftb1 and ftb2, hackers was warned :P
(what I would do ^^)