Menthod to redirect based on DYNAMIC IP list from external source...

I can think of 2 options that would be quite quick

1. Use iControl (SOAP or REST) to synchronise the IP's to your data group
2. More useful. Use a sideband connection to check IP's and then push them into an in-memory table. You don't need them to stick around, because as you said you redirect to a static page telling them to restart their browser.

H