I would say code it, but provide a timeout, and let the thing install even if it's missing something.

Oh, absolutely, I think I didn't explain that very well. I don't intend to prompt all users for the information, just want to tell them that an additional test is available and then have them run that test (with prompts) manually if they want. That will mean less people actually run it, but that's better than annoying everybody who attempts to install the module :-).