In Security Center v11 this is possible. However it appears you can't exclude specific files / folders from the real time scanning. You have to pick either i) All Files, or ii) Programs and Documents. It would be a big help if the real time scanning would also have per file / per folder exclusions.
Yes we have suggested it to McAfee. This is such an ancient thread the oriiginal poster will have to refresh his/her membership in order to respond..