How to transfer traffic from one NPM to another NPM

[2-MAdD]

My question is as followed.

I've got a NPM in my production network that is reachable via the outside world. This is handeling my domain.com traffic
Now i want to create a NPM in my UAT network, so that all traffic from UAT.domain.com is routed to this NPM using the production NPM (as i only got 1 external ip-address).

Thanks for any help setting this one up