Restrict dns queries to *.airdn.org for certain interface

[babobobom]

Hi,
I'm using pfSense to connect to AirVPN. In order for the OpenVPN connection to be able to connect to "xx.vpn.airdns.org" I need a working DNS server through the WAN interface.

But as soon as the openvpn connection is made, I'd like all dns queries to go over WAN_VPN instead, so I don't get DNS leaks.

Is there a way this can be accomplished? Currently I have DNS Forwarder to allow anything, and it works, but I have DNS leaks.

Can I restrict queries to "*.airdns.org" through WAN somehow? Or is there a better way to solve this?

thank you!