I thought of linking HS recovery to Endurance too, but in the end I decided against it.
It would greatly favor some classes over others (those classes who can train the skill without taking a feat plus those classes who have Con pegged as an important attribute).
I came to the conclusion any rule like this would work best if it was completely independent on class selection. (At least, as independent as any rule that modifies Healing Surges can get. However, whether my rule favors classes with few Surges or those with many, I cannot yet say).
Regards,
Z