I have the same problem with itemrack, so if anyone could post a way for me to get it to work with Itemrack too that would be great. I couldn't find a way to get it working myself but until you do or someone responds here you could use this macro..
Code:
#showtooltip Amani War Bear
/equip [nomounted, outdoors] Riding Crop
/equip [mounted] <trinket name>
/cast [nomounted] Amani War Bear
/dismount [mounted]
Just replace <trinket name> with whatever your normal trinket is that you use. It will equip your riding crop and mount up, then when you push it again it will equip your normal trinket and dismount.
Just noticed you edited and found it, macro will work for other people who want a mount macro anyways.