I prefer using a nipple driver specific to my chosen nipple but sometimes that’s not possible. Sometimes a tool doesn’t exist or isn’t available but you’d like to use one anyway — getting your nipples started evenly makes life a bit easier. In a pinch you can make one.
To make a universal nipple driver I trim a thin butted spoke and roll threads in such a way that the threads cross the butting boundary. This lets a nipple thread all the way through without bottoming out. Then I attach an inverted nipple — one with a round bottom and no screwdriver slot — leaving a bit of spoke thread protruding. How much protrudes depends on how far you want the driver to work. I use some Loctite so the nipple doesn’t move but a jam nut can be used if you want adjustment. In the following example I inserted the tool into a pin vise but you could glue it into a cork, dowel, etc.
To use the tool thread it onto the back of your nipple. Insert the loaded tool into the rim and thread onto a waiting spoke. Then sideload the spoke to hold the nipple and unthread the tool. This isn’t the fastest way to work but it gets the job done and costs very little. I keep a couple around for starting deep dish rims, where a longer reach is required and the risk of losing a nipple more acute. They’re a good solution for inverted nipples too.