Restrict relay to internet2

[Nathaniel Fairfield]

Folks,

I run a tor relay node (no exits) on my school's network.  Due to their 
bandwidth policy, I have to limit traffic to about 1 Gb per day.  Weak, 
I know.

HOWEVER, my school is also connected to the Abilene/Internet2 backbone, 
and they DON'T limit bandwidth usage over Internet2!

Internet2 is set up such that it is transparent to my computer, but I've 
hacked together a simple script that uses traceroute to figure out if 
traffic between my machine and another host is going over Internet2.
So I can scan through the directory of Tor nodes with my script, and 
find which ones are on I2.

The final part of my scheme would require that I be able to restrict my 
tor node to ONLY relay traffic to/from I2 nodes.  I can't figure out how 
to do this.

Anyone have an idea for how to pull this off?  It seems to me that I 
could do it with a lot of hairy routing rules, but this would be bad 
because I'd be breaking circuits all the time.

Thanks,
Nathaniel