Is it possible to alter variables in a caller()'s namespace?

I'm trying to write a common subroutine that will check authentication data (from %fdat) and control redirects (via %http_headers_out) This is a HTML::Embperl page, btw. I'd like to be able to just put in code similar to:

[-
  $user = Common->checkauth()
-]
[download]

Where checkauth will check the paramaters in %fdat, and if they match up, return a new logged-in user object. if they don't match up, send a location header, and exit() (which is handled specially by embperl

There's no reason why I coulden't just pass in %fdat & %http_headers_out, but I was just curious as if this way was possible solution

Thanks in advance