mmmm I like the way you think Euryleia. I assum the only part of the sub touching the wall is the fingers holding the coins. About two feet away, on toes and holding an enema with a butt plug would just make a subbies day. I would add a blindfold and a random amount of time so you don't know how long you've been in position, or how long to go.
I wouldn't just drop a coin part way in just to play with subbie's head. Evil grin