Add "command prefix" parameter or similar

[McGiverGim]

Hi! I've the next problem: I want to build i386 packages in a x86_64 machine. After some tests, the only good solution that I've found is to prepend setarch i386 to the command, so the command:

rpmbuild -bb -vv --buildroot ... behaves setarch i386 rpmbuild -bb -vv --buildroot...

Can you add some new option to your library that lets prepend "something" to the command? Or if you have a better solution it will be great.

Thanks for your library!!