I need to be able to add multiple overlapping groups without the need of defining a separate GPO for each combination. This rules out the standard "Enable Client Side Targeting" and the basic GPP registry setting as they both overwrite the previous entries in the TargetGroup key.
To this end I came up with the following idea.
Use group policy preferences to define a custom branch of the registry into which a set keys and values are written by GPP. The key name is the group desired, the data is a flag to make it active.
I then have a small executable on each workstation which (on boot, service restart, etc) reads these keys and (if an appropriate value is found) concatenates these into the TargetGroup key.
I could very much use a sanity check; is there any reason this would not work?