Where to put these flags?

Hi List I am currently adding cabal-install flags tell cabal-install how to compile the setup program (in case the "external method" is used. Now what should I do? Should I ... a) extend global flags? b) extend only ConfigExFlags? (which means users cannot cross-compile without explicitly calling 'configure', OTOH users can set these values in cabal config file) c) continue to add a set of flags to every command? My preferences: (b) > (c) > (a). What do you think? With best regards Sven Heyll