Relocating files

I am looking at relocating files (just to be clear files using a different directory structure at package construction time than at installation).

Using %prefix is undisirable cos it forces users to have to use the --prefix option when doing rpm -i which isnt really feasible in this case.

Using %buildroot is of no use because no part of the path at package construction time forms the final path at install time.

(1) Is there away to specify the install prefix in the spec file ?
(2) What other ways are available for relocating files?

Thanks for all interest