in reply to TDD of non-module code
I'm not sure if it's at all comforting, but you're running in to one of the consistent early hurdles of TDD as it relates to componentized (hush, it is too a word) architecture. TDD nearly demands you expose your code to the tests. I've been an aspiring TDDer for about five years now and still run into this problem like a skier hitting a patch of mud. I've finally convinced myself that the increased exposure pays off more in testability than the protectionism of hiding your deep implementation does in safety.
THAT said I like the command-line switch idea. What I most frequently do is push everything into a method (including an actual "main" method.) And I keep a "test" method as well. It's not particularly pretty, but then I'm certainly the only one who runs tests on my code.
At least if you had a testable mode selectable off the command line you'd be able to include your tests in a larger scale test environment.