Microsoft DNS: Provide different answers per-src-subnet to same query - do I need full split horizon/brain?

The bind "views" feature would do exactly what you want here but Microsoft steadfastly refuses to implement something similiar.

It sounds like subnet prioritization is the closest thing to what you're looking for. This setting causes the server computer to return "A" records to clients in the order that most closely matches the IP address of the requesting client.

Windows Vista and newer Windows versions do this to the results they receive from a remote DNS server by default (see http://support.microsoft.com/kb/968920), but setting this option on the server allows earlier clients to receive the "A" records from the server sorted by subnet. Be aware that there is an implicit assumption of /24 subnets by the DNS Server (see http://msmvps.com/blogs/acefekay/archive/2010/05/29/dns-and-subnet-priortization-amp-dns-round-robin.aspx for a lot of background on this behavior) unless you tweak the configuration.

You'll want to setup each subnet to it's own site in Active Directory. This way the users will receive the DNS response for their local subnet as the first IP to try and the other IP as the second IP to try.