build ghc package from repo ?

Dear ghc-users, I'm having a rather tricky time building a fresh copy of ghc from the git repository (let me call it git-ghc) and then getting my-own-client-code to compile with the modules from git-ghc. The catch is that my-client-code also depends on other cabal-installed libraries which break once git-ghc is installed as _the_ ghc in my system... Is there a way I can just build git-ghc but ONLY install the packages (i.e. add them to the ghc-pkg database) so that my-own-client-code can then be compiled (by platform-ghc) against the modules from git-ghc? Thanks!, Ranjit.