I was just looking at something similar, you do an AD Sync to bring these computers in to epo? In 4.5 (hopefully in 4.0) there is an exceptions list that you can not import that client in to epo. Also, if the client isn't running, perhaps their AD object could be disabled. That helps everyone know that status on the machine and EPO won't import it (hopefully also on 4.0). Good Luck.
Thanks! I'm not sure about an exceptions list... I will have to look for that. However, I do know that I can go into those reports and exclude certain machines from showing by saying "not equal to" and then the machine name. Not sure if that is what you are talking about, but I plan to look into this further today or tomorrow.