interface based VPN routing? IE select source interface

I’m looking for an elegant way to have 2x L2TP or PPtP tunnels sourced from different WAN interfaces for the purpose of redundant links.

I’m currently adding routes to 2 IP addresses on my remote side via each interface’s gateway. IE:

wan1 10.0.0.16 gw 10.0.0.1
wan2 10.10.0.16 gw 10.10.0.1

remote CCR for VPN termination requires 2 addresses to do this:
10.50.0.1
10.50.0.2

route dst 10.50.0.1 via 10.0.0.1
route dst 10.50.0.2 via 10.10.0.1

the problem here is that one or both of the wans can be dhcp, so needs a script to find the individual gateways.

I can’t do EoIP which does handle the source address interface routing (apparently) because I need to penetrate NAT. L2TP is ideal, PPtP is a second best

Does need to be a full tunnel interface because I use ipsec and bfd on the interface to do rapid failover and automatic routing.