+my $url = $conf->config('cust_main-custom_link');
+
+my $agentnum = $cust_main->agentnum;
+# like eval(qq("$url")) but with fewer things that can go wrong
+# and if $custnum isn't mentioned, assume it goes at the end
+$url =~ s/\$custnum/$custnum/ or $url .= $custnum;
+$url =~ s/\$agentnum/$agentnum/;
+