Here's one of those silly little things that I happened to stumble across, and really like. I found a nifty little clamp on Amazon that'll hold onto the dovetail of a PRO FIZ plate, and has a 15mm clamp on it. $22.90.
Originally designed to clamp onto a hot shoe, but for some reason, it's designed with a dovetail clamp on it. It's got enough room on the screw to easily clamp onto the PRO dovetail.
I've found most of the clamps from SmallRig to be better than they have any right to be for the price. The knobs are a little cheap feeling, and the overall quality isn't what you'd expect from an American made product, but this comes in at the "cheap enough for me to toss into the kit and not worry if it gets lost" price point. My Preston rarely gets used off my rig, so for the few times it does, this'll provide a nice option, rather than just bongo ties.
Just thought I'd share, in case anybody else would find it useful.