I don't believe that there is a Hex edit trick out there to mod the P1225 for more channels. There was an aftermarket add-on board made by Scholer-Johnson that added PassPort/LTR options to the radio, as well as boosting the conventional channel personalities to some high number. You could purchase that board (and the special RSS that goes along with it), but you'd end up paying more for all of that combined, rather than just getting a 16 Channel radio.
Hey, Dayton Hamvention is coming up. If you plan on going, (I know I am), you could probably get them there on the cheap.