First modify the properties of the VPN connection to not be used as the default gateway for all traffic.
1. Navigate to Control Panel > Network and Sharing Center > Change Adapter Settings
Still in the TCP/IPv4 Properties
5. Click Advanced
Next add routes for the desired VPN subnets. This should be done with the VPN connected.
Split-tunneling is now enabled for the VPN, however the routes must now be put in so that the remote clients are able to reach other subnets. By default, only the Client VPN subnet will be directed over the VPN.
1. Open an elevated command prompt (Start > search programs and files for "cmd" then press Ctrl+Shift+Enter you should now be prompted for a UAC)
Still under Elevated command prompt
4. Run the below command replacing the relevant information between the <> markings:
route add <destination subnet> mask <subnet mask> 0.0.0.0 IF <VPN adapter number>
The above route will be deleted upon a reboot.
To make the route persistent, append a -p flag to the command.
Credtis to http://community.spiceworks.com/how_to/show/75078-configuring-split-tunnel-client-vpn-on-windows for an awesome guide