Initiate of Ilmater feat :
"When you cast any cure spell that would cure more damage than the target has taken, the target gains the excess as temporary hit points. You can bestow a number of temporary hit points equal to the target's Hit Dice ׳ in this manner. These temporary hit points last up to 1 hour."
... gets into the ballpark.
Verdant Lord prc 8 :
"The animated tree gains a number of bonus Hit Dice equal to the number of verdant lord levels the character possesses."
... suspicious they fubar'd doing a plant Animal Companion port.
edit --- but obviously not what you want.
Lots of mount based stuff, which I'm presuming you aren't
edit = metoo
I shouldn't post late at night...