I wont lie to you, it was very difficult to position him correctly. Alot of other collectors that i've seen with the same display seem to not take much care in how the figure looks on the bike which makes it obvious that the figure doesnt belong with the bike and ruins the whole display. All i can say is to research into body positions of how the body would look when in the same seated position as Arnie and then try to recreate the same positions with the figure.
To answer your question in regards to the leather...i thought this myself when attempting to position the figure on my Harley as you really need to ben the leg area to get it to fit comfortably over the seat. Just be careful when you are doing this as there is always a possibility of tearing the material. I have checked my figure and there appears to be no wearig to the leather so its just a case of being very careful when extending the legs that little bit further than you normally would if you were displaying him in a standing position. Let me know how you get on