I would not ask them to 'do you a favor'. It is their favor for you letting them touch you.
I would just point and say 'right there, right there'
She is going to say 'what' or just understand and do it or refuse.
If she asks what just say again 'right there, right there'.
By this point if she has not gotten it yet, tell her,
'Scratch, right there'.
I bet she would instinctively reach out and do it since she just figured it out. No clue if any of this would work, but you would not DLV by asking.
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Recommended reading list.
Double Your Dating by DD
(This will work on your inner game)
http://www.freewebs.com/xfman/
(This will work on your outer game)