Limit Number of threads a user can have in a Forum

[Aspergillus]

Dear m8's,

We have a Section where some Special users can place their Ads.
In this Forum Users can Edit und delete their Threads with no time limit.
We realized that with a simple Plugi.

hook global_start

if ($forumid == 49)
{
    $vbulletin->options['edittimelimit'] = 0;
}

Now we'd like to limit the number of Threads a user can have in this forum (id49).
So users can have 3 Ads in this forum and none more. So if they want to add a new thread they're forced to delete an old.. bevor they can ad thenew one.

I was looking arround in the Add'ons section but cou'd not find anythin..
I ony found a Thread limiter that limits the amount of threads a user can start within a certain time.

So i hope someone can point me to the right direction?

Regards
Aspi