Sometimes when I'm having a very bad day warming up, I grab a 40-50 DB and goblet squat and just sit there for 30-40 seconds, pushing my knees out with my elbows, getting a feel for the bottom position. I think that works because my problems are usually more back than hamstring.
If it's a hamstring tightness issue, I think some big leg swings and some high knee running in place would work prettty well too. I used to do those when I had tight hamstrings before running or soccer.
I normally do bodyweight warmups and empty/ lightweight bar work to warmup, too. But, I hear you about when sometimes that is simply not enough for my creaky bones.
Hope that helps!