Right, or you could just do:

#showtooltip
/cast [target=player,mod:alt] Rejuvenation
/stopmacro [mod:alt]
/cast [target=focustarget,help][target=focus,help][target=target,help][target=player] Rejuvenation

That would basically make them cast rejuv on themselves if you hold alt and push the key, otherwise it would do the other logic path as earlier described.