If you don't want to do that, you could cut a hole in the back rest of the back seat, and then weld it back up when you're done. Ski passes are very tight.
Be careful doing that. In NZ for instance, if an inspection officer notices during bi-annual safety inspection, you would be required to have the repair certified by an engineer (at great cost) and a certificate of compliance issued as you have affected the structural integrity of the vehicle.
Other parts of the world may be different.
A good rule of thumb is, if it's metal, and part of the vehicle structure, and not perforated, don't cut it.
Also, South African cars have a fuel tank behind the rear seat so even if you cut a hole, the tank is still in the way.
Heaps of vehicles over here are condemned because some young fella cuts holes in the metal parcel tray to mount big speakers without realising the consequence (failed inspection, car ordered off road), and often the value of the car is less than the cost of having a repair done, and having it certified.