I had something similar come up on an NEC once -- the customer didn't want to dial 9 for an outside line. He had told the salesman, but it wasn't until we finished the install and started training that he told us. The salesman said, "Oh, I didn't know that was a dealbreaker!"
So on that one, we redesigned the ARS and made it work. What a freaking mess!
First choice to do it on the Mitel would be "Direct Truck Select" or "Direct to ARS" buttons, as John mentioned.
If the prefixes for your area all start with a certain digit -- say, "4" -- you could go to form 2, and make "4" the local access code for speed-dials, and then in form 31 assign a speed dial 9+xxx for all the local COs... Customer dials 465-7890, 4=speed dial, 65= 9+465, and the remaining digits SHOULD get passed to the CO trunk, but that all depends on the trunk, the timing, and the customer.
You could also make "4" a leading digit in form 26, and then don't strip it in form 22 -- customer dials 4+65-7890, system outpulses 465-7890. You'll still need a leading 9 for 9+11 and 9+911 calls.
Easier way is just to explain to the customer that he's taking a Porsche and asking you to make it work like a Yugo.
