Good suggestion though, just do it from the other direction and come in from Rannoch, stay in Ben Alder cottage, do the round, hike back out.
Don’t know what parking is like on the Rannoch road though, and it starts/finishes with a pretty boring slog up a forest road.
Although… do it from Corrour, hike up Uisge Garbh, climb shoulder of Ben Alder, descend to bealach and then to Ben Alder cottage, exit via bealach and Uisge Garbh again?
Still not sure of distances, arguably a more scenic approach than Dalwhinnie? (plus the huge bonus of not inhaling asbestos dust! 8) )