I have a 10spd road bike and know that on the X5 you can get a Saris mount that can hold a few of these bikes rather easily. I was thinking the same thing may work on the X6. I realize the back end slopes down, but so does the bike when you take the front wheel off and mount it to the rack by the fork.
No worries. I'm going to check the X6 out tomorrow with my bike so it will be easy to find out for myself.