What I want to do: Set up load balancer mode. I have 2 internet sources, a proxied WiFi connection from cellphone 1, and a non proxied tethering connection from cellphone 2. I want the proxy to become transparent to the clients, they will use both connections as non proxied. How can I set this up?
If I'm not mistaken, it is not possible to do that. The proxy runs on the client, not on the router.
I did some online research and found an article that might be helpful:
[OpenWrt Wiki] Tinyproxy.
I must admit that I haven't tried this myself, but it's possible that you could try filtering by the destination address to enforce the transparent proxy.