I had thought of something like the Wrapid Comb, but am unsure whether the thickness of the side would push the stock away and create cast on. Reading the link, it still isn't clear if that is adjustable but I am guessing that it is. Still, it won't give you the same effect as a MC stock. With an MC, your eye remains at the same height relative to the rib. If you raise your eye by virtue of am Adjustable Comb, something like the Wrapid Comb, CheekEze, or just by lifting your head off the rock a tad, the height of the eye increases relative to the rib which, as you know, results in a higher point of impact.
The virtue of a device, such as the 100 Straight or, I believe, the BumpBuster is that by lowering the recoil pad you raise the entire gun in relation to its mount on your shoulder. Some adjust as much as 1" with the result that you need not slide the gun as far up your shoulder to acheive a proper fit. This allows a trap shoorer to take a more erect stance than he might with another gun.
Actually, since I shoot trap with a relative flat shooting gun, a Citori XS Skeet, and want to be able to easily shoot skeet with it I may try the Wrapid Comb (if it can be configured so as not to add cast on).