Why not ask the powers that be to put a label on the URL indicating that that is where you go to manage your subscription, including to unsubscribe.
Lets look at the bottom of every email sent to the list.
Well, I'll be damned. I wonder what it has on it. From which you can unsubscribe. And here I thought it was one of the best responces to an unsubscribe message I have seen in a long time. You sould think that at least on the Sparc list you would get people smart enough to save the informat sent when you subscribe to the list, or at least read the subscription information at the bottom of each message from the list.