To make this job easier, I recommend placing a sliver of paper (approx 20mm X 10mm) between the body and steel back before starting. Unlike the marker pen, here you are dealing with liquid which makes the operation more prone to being messy. Place the paper over the vertical wire then attach the back. The paper which is now trapped by the wire and sandwiched between the body and steelback will help to avoid getting the nail varnish over the body. Try not to get build up on the paper.
Use a dubbing needle to remove excess varnish from the paper. You should run your dubbing needle completely around the back above the paper to remove any excess varnish. It pays to repeat this step while the epoxy is still workable to remove any varnish which may have run down onto the paper. If varnish is left on the paper, when this is removed you will end up with a ‘wing’ sticking out from the underside of the steel back which is undesirable.