Hi Simon,
I’m afraid this isn’t something that Viscosity supports out-of-the-box, however you can make use of Viscosity’s scripting support to have a third party tool trigger a Viscosity connection on a variety of different changes. The following forum post has some more information:
https://www.sparklabs.com/forum/t/auto-connect-vpn-on-specific-network/840/2
Cheers,
James