That's what I like about pipe clamps. Make 'em as long as you want, and with a couple unions, can add or subtract to fit. I have 6", 12", 24" and 48" pipe sections that I can assemble as needed (hint, using galvanized unions keeps the work off the pipe so you don't have to worry about it staining).
For smaller sections, tho, 1/2" clamps would probably work better than the 3/4" ones I use.
Go