I've not had a lot to do with google groups myself (yet) but I believe you can do posts from emails, i.e. send an email to the group and have it post automatically. You might have to set up another manger account or something though. Then you could set your proxy listing sites to post new proxies to subscribers (set a cron job I think) and subscribe your groups email to it.
That way you would keep sending new proxies to the group automatically every day, keeping the other subscribers happy (and subscribed) and may even increase the numbers if they get what they want, and all 'hands free' as it were. It may even increase in value too (fingers crossed).
Just a thought.
Or you could sell it as Zash suggested, or even auction it off somewhere to the highest bidder. I'm sure it would have some value to someone that wants such things. (just don't sell it to soldoni, I saw his dp post, what a dumba**)
If I can't be a good example, I'll just have to be a terrible warning...