Its specific to Tony Hawk and whatever games incorporate it. The reason why it would be hard to do is because when you launch a game... you lose control of any built in SIP keyboard.
Some games have onscreen controls like Tony Hawk, FPSce, NES emulators etc.
Most PPC games are touch screen sensitive so the support is there.
I know what your talking about in FPSce... but I think what your asking is if you can use FPSce's built-in controls in landscape mode?
Well I haven't played with FPSce much... but I have had my Axim for over a year and I know something that might work for you. Try this:
Switch the Axim into landscape mode before launching FPSce or assign "Rotate" to a hardware button and try rotating while in FPSce. The program may do one of three things...
It'll either be aware of the change and redraw the screen to best fit landscape and hopefully draw the onscreen controls on both sides of the screen... or you'll have a stretched portrait view... or it might crash.
I haven't played with it so I do not know about how FPSce plays with different angles. From what I know FPSce is just a hobby and not a full blown production we have to be happy with what we have. BUT the author of FPSce is a super nice guy and I'm sure onscreen controls wouldn't be too hard to implement because they are already there... you just want them rearranged so that you can use the hardware D-Pad and have the buttons on the right side of the game in landscape mode.
Like in this Pic?