I've done it in pfSense 2 Beta4.
Just in short:
First, it's not send vendor-class-identifier but send dhcp-class-identifier.
This is different from other dhcp clients, but using dhcp-class-identifier does send option-60.
You may also need other options. Just compare dhcp requests with a sniffer…
To get it persitent, you need to modify the /etc/inc/interfaces.inc file.
If you only have one external interface you need to find the place where it writes the dhclient_wan.conf file.
(this differs from version to version!)
Here you should find the lines that write:
$dhclientconf .= <<<eod<br>interface "{$wanif}" {
timeout 60;
retry 1;
select-timeout 0;
initial-interval 1;</eod<br>
You may add any line you like there.
If you have, like me, one WAN interface for internet and another going to the IPTV network and you only want the extra dhcp options on that one, you need to add some intelligence with something like:
if ($wanif == "re2") {
... (your modified setup)
else {
... (a copy of the original setup)
}
You will make any modifications at your own risk! Make backups!
One last thing, this modification will not survive an pfSense update!