So I get the basic gist of linking doors and zombie spawns.

My question is, is it possible to link a zombie spawn to different doors that use different links?

Here's some context:
You are in room A. There's a spawner in room B. The path from room A to room B has two purchasable doors (door 1 and door 2). I want the spawner to start spawning zombies whenever door 1 or door 2 is purchased. However, I do not want to link door 1 and door 2 together. When a player purchases either door 1 or 2, they'll have to purchase the other door they didn't purchase.

I tried setting my zombie spawner link/flag to "1, 2" ,but it didn't work. I tried "1 2" , but it didn't work. So is it truly impossible, then?