i wud of suggested the tow bar mounted like i use but youve alerady dismissed putting a tow bar on.....
just have the clips on the boot mounted one ripping chunks outa your paint work
you could always get a tow bar fitted, jus the mount on the chassis if you got 1 with the bolt on ball, remove the ball, leave it off and just have the flat plate there waiting for the bike rack to be bolted to it when needed.
bit of a faf like but ive seen the mess 70mph and a snapped strap can do to a (expensive) bike.