Why don't you buy a boot liner? I have one in my wife's Merc estate if I am using that, its designed to cover the entire load area with the seats down, laps up the sides of the car, and has a flap that comes over the bumper to protect it when loading. Just pop the from wheel off and shove the bike in, job done.
Something like this:
Volkswagen Passat Estate (Lowered Floor) 2015 - Onwards Custom Boot Liner
Something like this:
Volkswagen Passat Estate (Lowered Floor) 2015 - Onwards Custom Boot Liner