I use alot of weight with my BP/w, so I had to figure out some way of doing it comfortably. XS Scuba weight pockets from either LP, or Scubatoys work well for some of it. Scubatoys doesn't have them on their site, but will order them for you:
http://www.xsscuba.com/weight_belts.html (bottom of the page), the WB101 slides on your harness webbing, and the WB101Q, has a double velcro tab so you can take it off and put it on anywhere you like. I use triglides to hold two of the WB101's on my waist belt, right up against my back plate on each side. Nice thing about these, they are cheap, like $8 each.
That is only part of the solution however. Dive Rite makes trim weights
http://www.diveriteexpress.com/bcs/weights.shtml (about half way down the page). The holes didn't line up on my DSS SS plate, so I used some cave line to secure them to the plate, and then a line from one side to the other to keep them in one place.
This is in addition to 8lb weight plates that Tobin at DSS also sells. The nice thing about this rig, is now I have 20lbs of weight on my back, 6lb for the SS plate, 8lbs for the weight plates, and two 3lb trim weights. The weight is very even on my back as well. Then I can adjust the weight in my waist pockets as needed. I went to 20lbs because this is exactly what I needed wearing a 3mil wet suit with a Steel 104's in fresh water. After that, I just add weight to the belt. My trim is great with this set up.
Something I did for salt water with this rig, was to add a DR mask pocket to my right side. I usually don't have a need for a can light in saltwater, so the pocket helps with the routing of the long hose, and holds my mirror, whistle, safety sausage, gloves, and even wet notes.
Gooc luck.
Jason