You have 10 skill bars, 4 of them are vertical, unless your on PS3 then you have 8 double crosses, I sugest using on of the vertical skill bars put it off to the side somewhere and throw your mount on there, you'll have room for 12 there. It's what I'm doing and it makes things easier to call any mount I want. And becasue I don't have 12 mounts, I put random commonly personally used actions on there, like dye and summon my choco companion. If you have the will you'll find a way to make it work.