I had thought about this as well, or even making the entire syntax something like $x = $y =~ \s/foo/bar; or something of the sort. To be honest though, everything worked well when I posted this - and I didn't think I was actually parsing too much Perl on my own - but as I expanded, I realized what I wanted to - things like my $foo = sub_returns_string() \~ s/bar/foo/;1 just got too messy and needed too much parsing of Perl, so as much as I love this idea, I've dropped it - for now.
1It seems like there's just increasing complexity to make it 'just work' like people would expect it to. Something like my $foo = subroutine( this => 'contains an equals', $self->{ scalar @array } ) =~ s/a/b/g; although probably would be rarely used, would still need to just work. So I'm really beginning to understand why people shy away from using source filters, because really there is a lot of parsing Perl, even for the simple thing like I wanted to do, where I thought I could isolate the problem and not have to do much.
-Bryan