Some sort of roof rack that fits the existing bolt holes my 300ce roof exists, from the dealer; expensive as I recall.

Also, an Australian company named Rola is the only aftermarket firm I have yet found that sells racks that fit the existing bolt holes - the local outlet here in California emailed me they were looking for a new office space and would contact me when they found one...that was many months ago.

Good luck; btw, I wonder if the roof can be raised if a flat object is on the racks?