Isolating an SSID from all other SSID's and wired LAN

Can this be an option next to the Isolate Member feature

I know this can be done by VLAN, but i have already used all my 5 LAN subnets

I this this is the answer you are looking for
https://www.draytek.co.uk/archive/kb_vigor_multiplessid.html

Yes but this isn't possible on my 2925n+

But it should be isolated from both wired LAN and other WLAN SSID's

yeah it not possible unfortunately. VLan is the only way at the moment