Have you tried and/or considered a one handed controller?  They arent ideal for FPS, but certainly an improvement on not being able play at all.

I reckon your best bet is going to be a game where you can map the controls to your own preferences, alas I know of no games like this as I'm not an FPS fan.

Hey everyone, Im looking for some first person shooters for the PS2 where the use of both analogue sticks is not required. Something like the old Medal Of Honour games for the ps1 where you had to use the shoulder buttons to look up and down and X was shoot. My dad can't play with both sticks as he has a funny hand (paralysed and stuck in an awkward position) which means he can't use the right stick and shoulder buttons at same time.