No need for eval or other heavy artillery.

package TMPL;

sub fodus {
    local $/;
    my $out = <($main::{+(caller)[0]."::"}->{DATA})>;
    # ...
    return $out;
}
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The key here is that Perl makes the symbol table of each package available as a hash called %%packagename:: - with %main:: containing keys for all packages including itself, the value being a glob pointing in turn to that package's symbol table. So I use %main:: to get the glob to the caller's package, then dereference it as a hash, fishing the DATA key from it in turn.

Makeshifts last the longest.