How to disable only SSID1 on a Draytek 2865

I have a Draytek 2865 configured with three wireless networks: SSID1, SSID2 and SSID3. I need sometimes to have SSID1 off and SSIDs 2&3 on. At other times I need the reverse: SSID1 on and SSIDs 2&3 off. But it seems there is no way to turn SSID1 off on its own. Yes I could use SSIDs 2,3 & 4 (as they can be enabled/disabled individually, but then I have to have a fourth network, SSID1. I could hide SSID1 but it would still show up as a hidden network and any device pre-configured with that network would then connect.
So my question is can SSID1 be turned off (disabled) just on its own?
Thanks,
Mike