Control Group Solution Needed!

We are dipping a toe into the Control Group waters for the first time, in order to facilitate Plan usage across more departments.

Our Marketing department would like to use Plans to track engagement with community partners.  This requires a new set of Plan values, separate from the pre-existing plan values used by our Development department.

My needs:

• Hide Community Engagement plan values from Plan dropdowns if user group doesn't have access to plan value control group
• Hide Development plan values from Plan dropdowns if user group doesn't have access to plan value control group
• Allow users who cannot USE Development plan values to still SEE those values on a plan
• IE: The Marketing user who is responsible for maintaining the Community Engagement plan should not be able to apply a Development plan value to their plans, but they should to be able to view complete information on a Development plan.

My plan was to:

1. Create a Development General control group and associate it with all user groups that need to be able to create/edit Development plans
2. Create a Community Engagement control group, and associate with the Marketing UG that needs to create/edit Community Engagement plans
3. Apply the Dev. General control group to all Plan values specific to Development plans, such that Marketing cannot apply them to Community Engagement plans
4. Apply the Community Engagement control group to all new Plan values specific to Comm. Engmt. plans

The first problem I've encountered, perhaps obvious to those more familiar with control groups, is that when the Marketing user without access to the Dev General CG is looking at a Development Plan with Dev General CG'ed values, those values show up as their numerical ID number.

I tried associating the Marketing UG with the Dev General CG but unticking the Edit box - that brings back the visibility, but doesn't seem to restrict permissions at all. 

Is what I'm trying impossible?

Many thanks for reading and any insight!