Have you considered adding a floating-tab rule LAN->DMZ, with the "quick" option checked, at/near the top, without queuing options?
I think that it would then just go straight to the default queue, as any traffic not assigned directly ends up there.
The best bet that I know of is to make nested queues, similar to how the traffic shaper wizard does it if you use one particular wizard -- think it was the single wan/mutli-lan wizard.
Can't recall if it used the limiter thing and made pipes, or if it was some other method, but it's worth a try to run the wizards until you find the one that makes nested queues.