DNS hijacking & Tailscale

I've set up Tailscale on my OpenWrt router, following the instructions at https://openwrt.org/docs/guide-user/services/vpn/tailscale/start

The router is set as an exit node.

I'm also running https-dns-proxy for DoH support (with multiple dnsmasq instances), and have DNS Hijacking in place.

When I connect a client to my tailnet, and route traffic through exit node advertised by the router, the client uses the DNS servers from the router, rather than the Global Nameservers (https://tailscale.com/kb/1054/dns) set by tailscale.

How can I ensure that clients using my exit node, continue to use the Global Nameservers I set in Tailscale, rather than the router's DNS servers? I presume this is something to do with DNS Hijacking on the router, but I'm not sure.

What configs can I provide to help resolve this?