Multiple Wide-IPs with a single VS and Cross DC failover.

​According to your question i assume you don't have 4 free IP's per DC to separate your services.

You can create one VS per DC and segregate traffic by examining the URI and assign a proper Pool depending on the URI.

Do you want to initiate DC failover manually or automatic based on a health-check result?

If you need to failover automatically, do you want to do this per Service or for all Services of a DC together?