Summon random from unit list?

[Panpiper]

I'm looking for a way to create a ritual summoning spell that will summon one out of a list of a few different units. I would much prefer that this not involve overwriting other spells and units that might be used by another nation. I have spent an hour searching the forum and found no clue. It is perhaps not yet possible?

[Sombre]

Can't do it without overwriting.

[Panpiper]

Thanks Sombre. I guess I'll just have to make an 'imbue champion' spell for each power instead of having a single spell that summons a random 'commander level' troop. I still have no idea how many gems such a summons should be though. I'll start with five gems and wait for feedback I guess.