Multi route to outbound IP

First of all sorry for the topic, I could not think of anything more fitting. I will be setting up my OpenWRT Router next week and already panning out how i want to configure everything. Now I stumbled upon a question I'm not sure is doable (at least not with my limited knowledge of firewalls/routing/iptables).

One of my VLANs should only be able to access one IP address in the internet (Socks5 of my VPN provider). The issue is that there is a router in bridge mode from my provider inbetween that I can not cut out.

So the route should look like this:
OpenWRT --> Router in bridge mode (lets say --> Socks5 (let's say

So I would assume in OpenWRT I could only set the as allowed target for my VLAN port (in firewall rules/iptables?) since this is the next point in the network? Or is it somehow also possible to set a route + say afterwards only should be allowed?