Here is what has worked for me.

First go to Home Depot or wherever and buy a gallon of denatured alcohol and some rolls of those tough blue paper shop towels. Wet the towels with the alcohol and use them to clean up the epoxy as best you can after you join the wings, this will be sloppy and nasty no matter what but try your best to keep up with it.

Use the plastic bags the wings come packed in as a protective cover when epoxying the wing. Just slide them down over the wing halves and secure them with masking tape leaving only a few inches exposed in the roots so you can later clean up the epoxy ooze. This way any epoxy on your fingers wont dirty the whole wing.

Then after glueing and cleanup I like to set the wing vertical, allowing the epoxy to set. There will usually still be some spots of epoxy on the covering so I get it off by rubbing with the alcohol soaked towels, this works well because even set epoxy barely sticks to monokote.

And finally as you are gluing the wing and the epoxy is oozing take a second here and there to clean your hands with the alcohol, this will make it easier to work as your hands wont be sticky.

Hope thet helps!