I think something realistic would be a young and pretty unproven big plus filler to match contracts (if needed).
Something like Larry Sanders, Andre Drummond, Meyers Leonard or Enes Kanter. You'd have to go after someone with promise that has yet to be fulfilled, where a rival GM takes the sure thing in Rondo in exchange for potential that may or may not be reached in a big man.
Either that or a recent lottery pick like Harrison Barnes, that similarly shows promise, but has a few years to go to be able to reach it.