Just keep driving on the flat...eventualy the rims will cutt right through the tire.
abe

 

In theory, but I've got a 2009 Targa, so no roof-rack option.

Something like this but rather than a ball , it would be a riser going up up with 2 bolts to attach the old wheel too. (and the thing attaching below the bumper rather than through it. The steel bit would not be too big and bulky; something one could store on the floor under/behind the passenger seat.

 

Next, someone will be recommending the old continental kit modification!

 

^