2 bike rack on Brabus Center exhaust Cabrio?

Having eliminated the tow hook bolts as an option, does anyone have any suggestions. My goal would be to have something removeable with no visible modifications. The center exhaust would get in the way of a trailer hitch mount. The Brabus rear fascia is rather low and is one of the design elements of the car that I like so much. A small receiver type hitch on both sides of the car would not be objectionable.
A rack could then be easily inserted and removed, possibly a one piece inverted v shape with arms or clamps to attach two mountain bikes.