Practice a few times before you do it. Get some 1/4" flat bar stock from your hardware store, drill and tap a few holes. Place a stud below the surface of the 1/4" flat stock and after you've caught on to laying some beads ....practice
exactly what you're going to do. Make sure you get it right the 'first' time. I don't want to say you only have one chance.....but if you get it right the first time then you're golden. If not, you have more work. And welds are a lot harder to drill through!
The trick in my book is to learn to hit the stud right in the center with the weld wire, then keep on going, carefully spiral your way around the stud...from the center outwards onto the washer. You can clean the head area ahead of time with carb cleaner and
tape the washer over the stud ...you're going to weld to. Tape it to the head ...with masking tape. Once the washer gets hot enough to melt/burn the masking tape, it'll already be securely welded to the stud, so it won't matter. Don't use duct tape, that'll just make a nasty mess. But that's the trick...get ONE good spiral weld from the center of the stud and around to the washer. It's only like 3/8" and you want to get the spiral right. Then weld on a nut. You can partially tape that on too...once it's cooled down. It's all in a hard to reach area, so practice a little and take your time (even though the whole weld process takes 3 seconds!)
It's in a hard to reach area, so that's what makes it extra-fun