You are correct. All of the radio management features require WDS. I too am faced with the same problem of too many AP's on a subnet. I think my only solution is going to waiting for switch/router based WDS that can handle more than 30 AP's.
Also, I was told by a TAC engineer that you can go up to 60 AP's if the master is dedicated to WDS and does not server data clients. But, at ~180 AP's and growing that still doesn't help me.