I have been thinking about an interim solution, inspired by the fact that many architectures can run in either endianness. AFAIK, Virtual PC used this feature of the PowerPC to run Windows on a Mac. Apparently, Linux also supports running little-endian PPC binaries on an otherwise big-endian system.
It will not be as simple as compiling with -mlittle-endian, as the libraries should likely have the same endianness. It might be possible to cross-compile a little-endian system, compile a static binary in the chroot, and run the resulting binary in the usual big-endian system. Or it could be running in the chroot, if that is easier to accomplish.
So far, I have not managed to build such a system, but it might be possible with a suitable cross-compiler. I already use Gentoo and Crossdev for such things, but I have not found a suitable target machine type for this.