I was looking to do something very similar though I referred to it as a variable tier stand. Did a lot of searching and found a guy that was building a teeter totter style stand. If I remember correctly the MLT was in the center and the HLT and BK would travel up and down as required to permit gravity transfers. Never saw it completed so it may have padded seats on it now. I considered using some lifting mechanisms as well, and though I can fabricate, concluded the designs were all Rube Goldberg’s. I now have a single tier with one pump.