Check out this little contraption, a little over-engineered but otherwise 100% functional:
This is a picture taken while the wing is being dyed blue. All I had handy was some soft lockwire to build the prototype. I'd like to see if the hardware store has some lightweight aluminum rings about 3" in diameter, attach suction cups to that. I had to dip this disc 18 separate times, and one cup failed once, because I forgot to hold the disc instead of the device while I was having trouble removing all the little effing squares. That was with the cups on the other side, of course. That's why I made it 3 cups total, was for the underside. You can't have just one in the middle on most discs due to the nipple, and 2 doesn't give you 360 degrees of control while handling. Triangulation of the cups resolved the issue.