Timing is everything. I'm back at a long term client that had the same situation.

A long time ago, they had an Active voice that was replaced with an Amanda. It too needed more digits than the DBS would give me.

My fix was to chain-dial 2 buttons for VM access ACCESS

on/off
prog
pick a button X (usually 9 or 4, but be sure no one changes this one)
redial for pause
* ext #
Hold
(maybe add xtra pause @ start and between * and ext no.)

on
prog
button you want to use for VM access
conf
Auto
500 to vm
auto
90+ the X button
#
Hold

I presume you got the follow on ID, and forward thingies done already.

Always have enough fun to spread around.