I've never actually done what I'm about to propose, so there may be pitfalls I haven't thought of, but assuming that the assignment to my $res is the last executable statement in mydata.pl, I would try something like

my $whatever = do 'mydata.pl';
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That should be equivalent to assigning to $whatever the value returned by eval'ing the contents of mydata.pl.

I question the whole approach on design grounds, however. See this thread for some possible alternatives.