If I didn't get you wrong. you want to join your controlthink stick to your existing network as a secondary controller, right? If that's the case.
Here is the procedure
From the TE
1. Go to Settings Page
2. Click "Join or recover another network"
3. Choose "Join existing network" (this will put the controlthink stick in program mode to be joined to
another network. )
4. Do whatever you need to do to your primary controller on your network to include the controlthink stick.(this step is beyond controlthink's scope)