# how I do it now
$tmpl->param(flag_location => "foo $var bar");

# I have not used hashes here to make it easier 
# to see the two things I am trying to do.

# how I want to do it
my $param = 'flag_location';
$tmpl->param($param => "foo $var bar");

# or better still
my $param = 'location';
$tmpl->param("flag_$param" => "foo $var bar");