I had a very similar predicament to yours. I built my own stand for my 75G display many years ago before the idea of a reef tank was ever a consideration. I built it with supports in the center and then when I decided to start a reef setup, I couldn't get a big sump inside it. So what I did was use 2 tanks. I was able to get a 20g in one side, which has the filter floss, bubble trap, skimmer section and return. Then I built a small stand to raise a 10g tank up on the other side of the stand as a dedicated refugium, drilled it for a bulkhead as an overflow back into the sump, and split the return from the sump between the display and the refugium. The nice thing about a separate refugium is A, it's full to the top so it uses all 10g, as opposed to a refugium section of the sump which is usually only 2/3 full, and B, I can control the flow separately from the sump with ball valves on the split return.