It sounds like you have everything except an executable for the right CPU architecture, which is an integral piece.
If this .app contains compiled code, you are out of luck. If this is java or something interpreted (python, say) you could likely get it running. However, the chances are very likely that this is platform-specific compiled code since you said it is for intel machines. There will be nothing you can edit to make this run on your PPC machine. You would need to be able to recompile the source code.
-Lee