Slap me down if this sounds obvious, but wouldn't the cleverer thing to do here be to develop a Flash/SWF player for GP32? As far as I can tell, HL2D is made entirely in Flash, so a generic Flash player would be able to run it by definition, and also open up a MASSIVE potential area of expansion- think of all the Flash games & toys out there on the net already...
I'm not a developer, but I'm fairly technically-minded, and it seems to me that if SWF players can run on PalmOS/WinCE devices, then there's no reason why GP32 shouldn't be able to do it. the SWF format has (I think) been made open by Macromedia, and such a project seems to make so many kinds of sense...