Trade Tools are selling Omega jacks. Don't know how well these would last (Nick?), but jesus christ, their "1.5 Tonne Low Profile Jack" has a lowered height of only 63mm! Most low jacks I've seen are only 85-90mm fully down. Lifts to 500mm too, apparently. At $278 too, they're at a good price. If 63mm isn't low enough for you, maybe it's time to consider installing air jacks?