Canary How to heal player on top when player is in stack, even with hotkey or if rune is used onyourself

[ForgottenNot]

Hi

Would like to know if this if possible and if it's how to?
i use canary server, but a tfs uh rune would do the example too
i have this feature working in old server distribution with no hotkeys, so don't know if its possible to reproduce this when a player is stacked, causing to heal the top player instead of himself

can somebody give me hints on this?
at least in canary the spell ultimate healing looks like this so don't know what to do with it or even how to do something

local spell = Spell("instant")

function spell.onCastSpell(creature, variant)
    return creature:conjureItem(3147, 3160, 1)
end

spell:name("Ultimate Healing Rune")
spell:words("adura vita")
spell:group("support")
spell:vocation("druid;true", "elder druid;true")
spell:cooldown(2 * 1000)
spell:groupCooldown(2 * 1000)
spell:level(24)
spell:mana(400)
spell:soul(3)
spell:isAggressive(false)
spell:needLearn(false)
spell:register()

sieze the moment in order to avoid make another thread how to hit the whole stack of player when they are stacked using runes? and spells?