The trouble is, even that's not good enough. Someone posted a snippet on p5p in this thread, showing how the current incarnation of Switch gets tripped up by thinking it's in a string instead of code, or vice versa.

I don't think that's much of a problem. It's not that your code is different each time it's run. Your code is fixed, and each time it's run, it's the same input to the source filter. It's simple to test see whether the output is correct, or garbage. If the latter, fix your input, or fix your filter.