How to avoid Double NAT?

I have a modem/router supplied by my ISP. The optical fiber coects to it and Inteet and telephone lines come out of it. Unfortunately, the DNS server settings on ISP router are fixed and caot be changed. This is the way ISP ensures that specific sites can be blocked if any govement regulation comes in (Dumb... I know).

I want to use Google DNS/Open DNS for my network so I had two options - change DNS setting on every device which coects to the router or set up a router in front of it and set DNS on it. I opted for second option but this had led to Double NAT situation. Port forwarding has become a pain.

Is there any other way I can change DNS setting globally without making my network double NAT?