You can use HPCs, but I would suggest adding them to the health bar immediately.
Its a stupid suggestion, I know, but I think that having HPCs increase your life instantly would be a more rewarding twist, even if you have 3 and a quarter heart containers, or whatever.
Not a bad idea, but my opinion is that there should be a difference, because before entering the next dungeon, a player could be more encouraged to look for just one more HCP if the HPC slot already is 75% full, this isn't the case if there's an instant reward that would make the "HCPs" be more like regular heart containers.
Generally I enjoy to look for all kinds of treasures even if their don't make a difference until collected a given sum of them.