Weird question,. but is there any feat or magical item that can turn excess healing into temporary HP?
There's the feat Lifebound which specifically does this.
Aw. I was excited until I saw the limitation of "half your level". Who ever thought that would be remotely worth a feat?
There is a team feat that lets you pass excess healing on to others with the same team feat. But the range is like 5'? Honestly none of these feats are worth doing.
I'm using that on my Sacred Huntsmaster (of Vildeis) with Healer's Hands to burst heal both mount and rider. Luckily there's no arbitrary limitation on the amount of excess healing, so when my Inquisitor heals for triple their own HP the rest goes to the tiger.