I know this has been discussed before but i'm failing to either understand fundamentals or just tie it together.

I'm using originate to submit a tiff to the txfax application. No problem there.
In my originate command i'm also setting a custom variable called "realm" which  I use to tie an originate command to a customer. 
So i was trying to match the realm in a dialplan and set a bunch of other variables per realm.  I believe that  I cannot use the custom variable in the dial plan to match on in an expression search..  So..  I'm kinda stuck and looking for suggestions.   I really dont want to set all the variables in the originate command in this case.

thanks.

Juan.