You could look into Filter::Simple, but you'd need to be very careful.

And to save everyone the bother, many people say you shouldn't ever use source filtering in production code.

I think that's like saying you should never use goto. Of course you should *rarely* use goto and if you don't understand why goto is considered so harmful then you shouldn't use it until you do. I think source filtering is the same. (cf the recent discussion Re: Breakin' the rules, Breakin' the rules)