getting the -B topdir for a GHC-API app

What is the "right" way to get the topDir for use with the GHC API. I have a little app that I would like to cabalize and release, but I am not sure what is the approved way of getting the '-B' option set-up. I think it would be great if I could use template-haskell to insert the topDir from the ghc used to compile the app, but I am not sure how to get the topDir from the compiler. Is this possible? Does cabal already provide a means to install a "driver" script like that used for the ghc suite? Also, I am looking for a code-review. If you have some time, I would love some "style" guidance. The work in progress can be found here: http://mathewmills.com/runTests/runTests.lhs