We put this on the vpn server (which functions much like a home router, doing NAT and dns resolving)
iptables -t nat -A PREROUTING -i tun0 -p udp -m udp --dport 53 ! -d 10.53.1.53 -j DNAT --to-destination 10.53.1.53
iptables -t nat -A PREROUTING -i tun0 -p tcp -m tcp --dport 53 ! -d 10.53.1.53 -j DNAT --to-destination 10.53.1.53