Getting subzone of guildmate

[anathemort]

Is there an API for getting the subzone ID, index, or name of another player (particularly a guildmate)?

I know we have GetGuildMemberCharacterInfo(), which returns the zoneId, but that's going to give me (for example) Reaper's March when I'm standing in Rawl'kha. There's also GetPlayerActiveSubzoneName(), but that applies to the current player or "self", and I haven't found a way to get a "self" for a guildmate.