Expensive (around 200 €), but a perfect solution… from Park Tools – called PRS-4W-2.
The wall mounting plate is 15cm x 6cm and fixed with two mounting bolts. The stand uses what Park Tools calls “the 100-3D Micro-Adjustable clamp”. This clamp allows adjusting the clamping pressure in a very sensitive manner. I use the seat post of my Brompton to mount it.
The stand is a rock steady solution – quick entry and no legs to run over. I like it a lot.