As I don't have time to get into the code of the PSP, I am wondering, if it is not an easier approach to have lower firmware version (lets say 2.71) have a file code having 3.0x (assuming you have a 3.0x-1), where the update utility will accept the update, as it is a higher version? I understand that it is likely not signed code, so it might not be possible, but to me it looks like an option worth looking at (Likely it already has been).
Is anything known about the Signing of code process? I heard somebody mention a Sony PSP Devkit. Which would create signed code (likely you would have to be a Game-developer to get it, but still).