Static IP - Single account: Reverse proxy to new server?

Server 1: running WHM with a cPanel account at static IP address a.b.c.d - a Wordpress multisite 'hosting' client websites using their own domain names. Server 2: will pull the cPanel account transfer from Server 1 - but will not (yet) have DNS updated for new static IP address w.x.y.z (different network/subnet). So Server 1 cPanel account will be suspended, but Server 2 will not yet be routed to by DNS - only available via IP address. Many of my clients use my custom nameservers so for me to change the A record there, it is trivial. Some clients, however, have complex DNS and prefer to keep control - so for them I had to tell them to set their own A record to the static IP address a.b.c.d To give me time to have those clients update their A records to the new static IP address, I want to have Server 1 route all traffic for a.b.c.d to w.x.y.z I found this: