Yes you can waitlist for an upgrade with miles, just like with SWU. Difference is, as mentioned above, that mile upgrades won't clear at the gate and won't get you any higher upgrade list priority at the gate... it will go by your medallion status if it doesn't clear ahead of time.
Call up again and request a to be put on the waitlist for mile upgrade. Since you're over a month out, it is possible some inventory may open up as you thought.