Fantastic tips here.
After playing with everyone’s suggestions here’s the sequence of steps I found works pretty well and it avoids affecting both sides of the object.
- While in edit mode mask entire object by ctrl-clicking outside of the object.
- Select desired alpha.
- Press W to enter Edit-Move mode.
- Press ctrl-alt to draw one or more white inverse alpha masks on object starting either within or outside object depending on where placement is desired. You can switch alphas at any time to get different inverse masks.
5.When you have all your masks in place press Q to enter edit draw inflate/deflate mode and paint on your desired depth. You can also smooth using shift key while drawing in Q mode or use the deformation tab items for further modification of the Inverse (i.e. unmasked) areas. - Ctrl-drag small rect outside object to delete masks.
Voila.

