Drop sets is my answer to "no spotter" when I can't complete a set at higher weight. To do full-on mult-drop sets to failure, however, I think these need to be done with some recovery time. I've got the tendonitis to prove that.
Otherwise, esp on the big lifts, eg. leg press, if someone can strip your weights for you, damn. I haven't had a killer glute burn like that in looong time!