Celeron M to Pentium M...Impossible or Not?

I know this kind of question is asked ad-nauseum on this board and I have read through many posts, but they are usually issues of people wanting to turn PIII into a P4 or something like that which obviously couldn't work. My question is reguarding the post which said something to the effect that it is impossible to change processor families. I have a Gateway 4024GZ with a Celeron M 360 1.4GHz. I have checked out all the specs of my laptop and compared to the next-level up model 4524GZ which features a Pentium M (i think 705), and found that they are identical except for the processor. They both have the same i855GM/GME chipset, the same BIOS, and the same integrated features, in fact they both look identical. What would be the reason why I could not get myself a Pentium M 705 and stick it in there? The current CPU is in a ZIF socket, and from all the info I can find this was the only 4000GZ model with a Celeron M, so from a purely production point of view, it seems like Gateway wouldn't make the CPU removable unless they used the same motherboard to host Pentuim M's....