[Exim] combining variables into single key for lookup

Hello,

I have a module I have added that encrypts what you pass to it, and returns
a hex string. I need to combine two variables, in this particular case,
$authenticated_id and $tod_full. So far, I haven't figured out how to
combine these two variables in such a way that the lookup module will see
them as a single key. I don't want to fiddle with making the module do
query style lookups.

TIA,

Peter