I already shift my bikes down to Glentress on a regular basis on the back of my 250cc scooter. Loads of folks are impressed and ask how its done.
I strap a rack over the passenger seat, take the wheels off my bike and lay the frame on its side headtube to the front then place wheels on top and strap down with bungee hooks. Good for 70mph plus without any problems.
The illustrated bikes would probably fall foul of the law as mtb wheels are obscuring the number plate/rear lights. My mtb is secured above and well clear of lights and plate. The contraption will be seen at the MacRetro meet at Glentress on June 8th if not before !