Yeah, using Monokote is nicer, but tape is quick and easy, especialy when you don't know what the covering on the ARF is.

I cut a piece longer than the gap. I have my wife or son hold the aileron at full deflection. Then I stick the tape to the trailing edge with the ends I am holding curved up in the air. I take some scissors and trim off the finger print section, then smooth the tape down on to the aileron. I slowly bring the aileron up to level and run the tape down in the hinge line.

After I do both sides, I flip the wing over and tap talc or cornstarch into the hinge line to coat the tape so it doesn't creak as the ailerons move. I turn the wing back over and tap out the excess and I'm done.

I can do this by myself if I hold the aileron fully deflected with my belly, but if it slips the tape gets stuck in the wrong spot and I have to do it over again. I guess you could clip a weight to it. A couple of extra hands works better, but since it's on the bottom and doesn't show, I am never too worried.