On random maps there could be sections for players to buy health with energy or crowns. Those sections should not be present on all randomly generated maps, just sometimes.
Payment would be per health bar or for full health. There could also be an option to heal the entire party for a rebate or so.
It can have different themes. For example a friendly Gremlin Doctor or a well of some sort (e.g. healthy water pumps, operated with energy).
Also, an energy gate with a single love puppy behind it, would be an option, though evil teammates could kill it (and they probably will).
Maybe one of those flying skulls from the subtowns could be present and sell vials or vitapods, too.

It is aimed at helping rich but weak players, when their party members quit supporting them or when they feel ashamed for dying so often and want to stop draining the lives of revivers away.

Also it can be helpful in front of some danger rooms, if a player would like to enter, but thinks he is too low on health.

//edit
An energy gate should prevent monsters from hurting players while they are inside, buying health.