use IO::String;

...

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

sub evalCap
{
	my $code = shift;
	my $str;
	my $str_fh = IO::String->new($str);
	my $old_fh = select $str_fh;

	eval $code;	

	select $old_fh;
	$str;
}