Limit access in a Virtual Report Suite

We created a Virtual Report Suite with limited data access so one of our partners can create workspaces on their own.  I created a group specially for these people.  One of the hang-ups we are running into is when they create a Workspace Project and want to share, they have access to all users in the Org, not just their group which is a big security concern.  We do not want users visibility into all users.  We'd like to see it limited to the groups the "sharing user" is a member of. 

Example:

There  are 200 users & three Groups in the Org; GroupA, GroupB & GroupC. UserA is a member of GroupB & GroupC that have 15 & 20 users respectively. When UserA creates a workspace project and shares it, they should only be able to see & share to the other 34 users in GroupB & GroupC.