This is what I do in a hurry with floating clamps - pull both center mains on the same pull and clamp at the start of the mains. Don't move this first clamp
Now, repull one side and clamp at the bottom of both mains. Go ahead for another two mains on that side, each time moving the second clamp.
Then go back to the untensioned center main, tighten this second main, remove the first clamp, and reclamp at the end of the center mains using the first clamp - continue until done.
You will get a slightly loser tension in the middle due to the half-tightened inch of the string at the top of the first mains, but I could not feel any difference. If you are really picky, yuo could increase the center main tension by a few pounds on the first, combined pull.