You cannot change the external IP of the node, it will just bind to whatever the actual current WAN IP of your server is.
What you can do, which is what I am doing with two different nodes, is attach a domain name to your host such as Digital Ocean, and create two A Records. One for each of your nodes external IP.
us-east. points to nodes WAN IP
us-west. points to nodes WAN IP
Hope that helps.
Edit #1: Just saw floating IP. Have not used it yet but it should be doable with the example above to do the following:
us-west. points to Floating IP
WAN IP points to Floating IP.