If you regularly haul that many bikes you need to do what's necessary for the task. If that means buying a receiver so a hitch-mount will fit, that is what I'd advise. It's the best way to minimize the possibility of damage from a trunk-mount rack and/or the bikes on it. Check your local junkyards; you might find a sedan like yours with a receiver for cheap. Do the same for the next vehicle and move the rack to that one when the time comes.
I tend to get minivans and I buy used. The last one had a 2" receiver that I used a lot and when I replaced the van the next one was the same year and also had a 2" receiver already installed. Shop wisely.
Draftmaster Racks