The click nuts are nice - but if not an option, The APC racks come with a little spring steel tool that works ok. A thin flat-bladed screwdriver can also be quite handy depending on the nut you use.
Hooking one side in the hole, and the the tool you rest on the other side of the hole and basically slide the nut along it till it covers the other side you pull the tool out and it springs into place (in theory at least).
I have found that actualy finding decent nuts that work well with your specific rack is the most important. The small differences in vendors can make an easy job a real PITA, and influence the amount of blood loss during server installs