Automation available from wowace.com -
http://files.wowace.com/sw-a.html can help you. Among the things this wonderful mod will do it has something called loner mode , which declines all guild invites.
My favorite feature is that it does a who on all incoming group requests. It will also auto accept rez's, release in bg's, skip npc gossip and more.
It's worth a look.