The fly in the ointment is weight of the enclosure of the back-up batting. With lots of money but little storage space for a second quilt, I suppose you might make a slip cover for the climashield insert out of super-light weight (.6oz) cuben, perforating it for vapor flow. Using 4 sq yds of cuben for the pillow case, you'd be packing 2 1/5 oz of non-working fabric.
Venting of a too-warm UQ is fine, but it is fair enough to ask: What about concern for weight and bulk on the trail (or bike)? I'm personally at an OK compromise point with a 20F partial UQ.
I am surprised to read the number of folks using UQs at 60F+ or warmer. Maybe in another thread: Yes you can vent a 0F (down) UQ for 70F......but why did you even deploy it at that temp?
To the OP: Find a recent post by BillyBob on his early limited-run and discontinued Warbonnet synth-filled Yeti. It was zippered for additional seasonal insulation pads.