Hello,
Yes, I agree this workaround is not very flexible.
If you have a switch between the AP and the router, you have to configure the VLANs to match between the AP and the switch on the one hand and also between the switch and the router on the other hand.
The AP M220 can support multiple VLANs on its single port. One VLAN is untagged (also called native VLAN or PVID on some switches) the rest of the VLANs are tagged.
https://support.hpe.com/hpesc/public/docDisplay?docLocale=en_US&docId=c04483535
on page 75 you can find which options do you have for the Ethernet configuration (Network ->IP ->Ethernet Configuration). You can specify the Management VLAN of the AP and the untagged VLAN. By default the management and the untagged VLAN is VLAN 1. You can change them or you can disable the untagged VLAN which will make the AP send all the frames with a VLAN tag.
On page 34 you have all the options in the menu Wireless ->Communities. Here you can assign the VLAN to the SSID ( specify the VLAN ID to which the AP is mapping the wireless traffic when it is forwarded to the LAN). You can specify different VLAN IDs for different communities (SSIDs). All the VLANs expect the VLAN that you specified as untagged in (Network ->IP ->Ethernet Configuration) will be sent out with a VLAN tag. Or if you disabled the untagged VLAN all the VLANs will be send with a VLAN tag. The port of the switch has to be configured accordingly.
Assigning a subnet to a SSID is not done at the AP level. The AP is a Layer 2 device which has an IP address only for management access, no separate IP is assigned to every single SSIDs or VLAN. The IP subnet is assigned at the router.