Cavalier playbook please! Actually, that sounds like a compendium class rather than a playbook. Well shucks, I guess I should put my money where my mouth is. How does this sound?
When you bolster your relationship with your mount, you may take this move the next time you level.
Time in the Saddle
Write a new Bond with your mount, this Bond can be resolved as usual if you so desire. Whenever you write a new Bond you may write it with your mount.
Once you've put Time in the Saddle, the following moves count as class moves for you. In addition to your normal list of moves, you may choose from this list when you gain a level.
Practice Makes Perfect
When you bolster your relationship with your mount, add your bond to your hold.
Two Heads
When you make a move that involves your mount, you may roll +bond instead of the normal stat.
Do the Same for Me
When you are incapacitated, unconscious, or dead in the presence of your mount, your mount can make basic moves on your behalf.