Although the "eeg" trick of Abigail-II is nice, I don't think it gives you enough flexibility. I would use a sub, like so:

sub process {
    my $src = shift;
# possibly do some pre-processing on $src here
    my $value = eval $src;
# possibly extra external logging if something went wrong
    return $@ ? "<B>Error in '$src': $@</B>" : $value;
}
[download]

and then have:

$data =~ s/<# (\{.*?\}) #>/process($1)/eg;
[download]

Liz