What you need is an old front hub with QR (or mega cheap 2nd hand), U bolt or stainless jubilee clip, and length of unistrut. Using U bolt/clip attach the hub to the unistrut and thats it! Lay the assembly across the back of car/van/pick-up/trailer deck and you have QR mounting point for forks to support your bike upright. Just leave in garage or wherever when not in use – Simples!
I have even made a roof rack this way (20 years ago as poor student!)- BTW; if anyone starts making these and flogging them I want a cut 🙂 !!