I used to do this alot for customers, back in the ninties, and the filtrations typically were very high, 100 mag, 130 yellow, and sometimes I needed to add some extra using either the built in dichroic, or a filter gell. Another way to help is to put a piece of clear orange film base under the diffusor, and this will help to get your filter numbers back to a more managable level. The film base will add density, so you'll have to compensate, I think one to one and a half stops extra, but as I said its' been a long time!
Keith