You can make a nipple driver out of an a flathead screwdriver, if you've got a grinder. Grind the edges down so it seats nicely in the spoke nipple.
For getting the spokes in without getting them stuck in between the two walls of the rim, just be careful. I built up a wheel with a Mavic MA3 over Christmas, and stuck each nipple on the end of my adapted screwdriver and put it in vertically, so the hole of the rim into which it was going was pointed down (6 o'clock). Deep-V or aero rims will be more difficult because there's a lot of room between the walls of the rim.