In the CI Community @chicoscai had asked if it was possible to create Shared Control Groups. I too am searching for the functionality in CIS 6.4. It appears that control groups are only created out of a given segment. My department is manually lining up several test groups with a single control group for the Analytics Team. It would be great if the linking between Control Group and multiple Marketing Cells was possible.
Say for example if a split node could have a hold out group that is linked to all of the cells that come out of the split node. Or to have a control group node that would be able to look at all cells downstream that land in a communication node and record a link to them.