What I've been doing is cut about 7mm off the threaded end of a stainless steel spoke and screw that into the nipple leaving about 2mm out so that I can grab it with my finger tips. I then drop that into the rim space and using one of those strong "fishing" magnets draw it round to the hole. Then a different magnet to pull it through the hole. Next grab the nipple with needle nosed pliers and unscrew the piece of spoke. Keep hold of the pliers carefully and feed in the spoke and then turn the pliers a few times till threads have engaged. This is the tricky part - when feeding the spoke into the nipple, you can lose it in the rim space. You also end up scratching the nipple or squashing it if you grip too hard. Yeah, takes a lot of patience and having to put mounting frustration to one side.
What I've been doing is cut about 7mm off the threaded end of a stainless steel spoke and screw that into the nipple leaving about 2mm out so that I can grab it with my finger tips. I then drop that into the rim space and using one of those strong "fishing" magnets draw it round to the hole. Then a different magnet to pull it through the hole. Next grab the nipple with needle nosed pliers and unscrew the piece of spoke. Keep hold of the pliers carefully and feed in the spoke and then turn the pliers a few times till threads have engaged. This is the tricky part - when feeding the spoke into the nipple, you can lose it in the rim space. You also end up scratching the nipple or squashing it if you grip too hard. Yeah, takes a lot of patience and having to put mounting frustration to one side.