Otherwise, what about the kind of display wall that some people use, that is like a roller blind? If you fixed it to one of those sloping ceilings, when you pulled it down, it would hang straight.
I like the idea of a roller shade...or, since your DH is so clever, he could make a rigid frame that is hooked to the ceiling on one side with hinges and the other side can be raised/lowered as needed. When lowered, it would hand straight down for you to work on and when raised be flush with the slanted ceiling - use cording for raising/lowering and tie to brackets on the wall to hold in the closed position.