Using off camera flash getting full body shots

I have several strobes (3 430EX & 1 580EXII) & a few 33in shoot thru umbrella's & these are great for head shots & waist up shots.

Now if I wanted full body shots what would be the best course of action?Just use the flashes only & no umbrella?

I was hoping 1 flash to light the back drop.1 for hair light & hoping the other 2 flashes would be strong enough to light full body?Perhaps 3 flashes to light the subject(person)?

Any advice appreciated

How about stacking two umbrellas along the length of the subjects so that you get even coverage from the head to the feet?

Or a bigger umbrella.

I've used a 48 inch umbrella with a 580 EX II before and it seems to work fine for full body, not the best, but it works okay.