Program to tunnel IPv6 packets over IPv4 between isolated parts of campus network

I have a sixxs tunnel on one part of my campus network.

Meanwhile in a different part of the forest, I have a small network of 
hosts that can handle IPv6, and would *like* to have access to the 
greater IPv6 world, but their connection to the part that has access to 
sixxs goes over links that only support IPv4.

Is there a program I can use to tunnel IPv6 packets between the two islands?

Thanks!

Rick