My suggestion is to practice it outside of the water first and to do everything like your the 6 million dollar man in that slow motion action - slow and deliberate. Practice like this:
2 people, one to be the instructor (or a place holder for which) and the other the person having trouble. Have the student breathing from a regulator the whole time.
1. Eye to eye contact established (instructor points at eyes the student, student repeats in acknowledgment)
2. Instructor signs to remove mask for the drill, student ok's
<6 million dollar man time>
3. Student puts both hands on mask
4. Student removes mask with both hands then holds out in front
5. Student lets go with right hand, ebends arm at the elbow and lowers slightly.
6. Left hand moves mask over bent arm then lowers so the mask can be hung in the V of the elbow then release mask.
7. Hold left hand out and count on fingers 1, 2, 3, 4, 5.
8. Grab mask with left hand and remove from the V, when its clear of the right hand extend the left arm all the way.
9. Extend right arm to the mask and grasp it, return it to the face, and replace the mask strap over head.
10. Clear mask.
11. Locate instuctor and signal all is OK.
This worked out really well for someone in my OW class. We all took turns with the person, the rest of us playing the instructor role. It took about an hour and a half total, but the individual got it and performed wonderfully underwater. For us, it gave us a break from the pool water drills for a few mintes to rehydrate, change tanks, adjust gear, etc.. so everyone benefitted from it.