[Haskell-cafe] Cabal: disabling -fvia-C

I hope you will pardon another *ignorant* question. 'cabal install lambdabot' fails on Ubuntu Natty. According to the following exchange and bug report http://comments.gmane.org/gmane.comp.lang.haskell.cafe/88735 http://hackage.haskell.org/trac/ghc/ticket/5050 the workaround is not to use -fvia-C. I have found an {-# OPTION -fvia-C #-} deep inside the lambdabot code in Plugin/Pl/Common.hs. How can I tell cabal install to ignore this? Is there some command line option for doing so, or do I have to edit the source code and somehow persuade cabal to use my hacked version ?