[RT#89843] Here, have a patch :)

Make callsite take a parameter similar to caller, which indicates how
far up the call stack to go before returning the callsite.

This is a lot less complicated than it looks. Most of the patch is just
the implementation of Perl_caller_cx from 5.14.0, since earlier versions
of perl didn't have that function in the API.

Since it seems (meaning no disrespect) that I am in fact doing all the
technical maintenance on this module, I would be willing to take over
CPAN maintainership as well if you'd like. (Or not, of course.)