Make some daemons use different default gateway, and hide some interfaces from them

I want daemons like tor, dnscrypt-proxy, etc. to see only certain network interfaces and use a different default gateway than what is set on the router. There is no way to configure Tor to use a different route, only a different source IP address (OutboundBindAddress in torrc)

I found out how to use 'ip' to create a new netns and create an interface in it, but I read that I cannot just "share" a network interface with another namespace.
I want to avoid creating a new wireguard interface for each new namespace because that might be seen as unique sessions by my VPN provider, and they limit sessions to something like 3, so I would like to avoid creating more sessions to them than I need.

Aside from that, I am doing this because it would just be nice if some daemons cannot see 'wan'. Before I used OpenWRT, I would set iptables rules that match their UIDs, blocking them from outputting on some net interfaces. But I was never able to change the routing table for just a process/uid/etc., and kernel namespaces seems to be a way to do that. I want to know if there is an established way to do this in OpenWRT, and if not, any help would be appreciated.