I actually do it with a back brush that has a sponge on it instead of bristles. It's a bit messy so you really need to be in the shower to do it. I put the lotion on my shoulders and upper back and the go for the slather. I did try a brush with a hollow handle once, but the lotion was too thick to go through the sponge unless it was the density of liquid soap.
All the best with your efforts.