Overlandnoob, the Omeo-Bright-Omeo bus Monday, Wednesday and Friday gets you part of the way. See
http://www.omeobus.com.au/timetableA taxi goes Mt Beauty-Bright-Mt Beauty, meeting the Vline coach. This is a conventional taxi, and I think they have a mini-bus as well. I've taken this taxi to Bogong Village, and it should be possible to keep going to Falls Creek.
MB Taxi service, 15 Freeburgh Ave, Mount Beauty 03 5754 4735, 0409 573 909
Your best approach may be to contact the Mount Beauty taxi and see about a charter Hotham-Falls Creek. It may save time at the end of the trip to park at Mount Beauty and take the taxi to Falls Creek. Or you could go one more step and park at Bright, taxi to Falls at the start, then a short taxi ride back to Bright at the end. If you return on the Wednesday, the Omeo bus leaves at 9.30am, costs about $5, maybe 10% of the cost of the taxi.
If doing that and going on the AAWT, last night at Derrick and an hour to Hotham, pickup at the visitor centre. These are good drivers, and have dropped me at places away from the regular stops. Or you could make the last night at Federation Hut and race down Bungalow Spur to catch the bus, or go to Harrietville Caravan Park and sleep in.