If you're not using a can light, have you considered keeping the ACB and adding more weight directly to the harness waist belt itself?
When I'm in singles, I'll use the ACB pocket on the left side but not on the right side because I use a canister light. I'll just add weights to right side next to the canister and retain everything with a buckle. I can envision adding weight to the left side next to the ACB, which would be non-ditchable, but fine with me. I can easily add 5 pounds or more to each side.
Obvious question - what about a weight belt? I don't use them myself, and often ride higher than my harness belt anyway.