After almost 2 hours I figured it out.
Step 0. In your UE4 project, open the Project Settings, go to Description and fill in a Project Name, in my case “VirtualStudioProject”
Step 1. Pair the Tracker with SteamVR, and rightclick it and select Manage Vive Trackers
Step 2. Give the Tracker a Role, in my case I choose “Camera”, click Close
Step 3. Go into SteamVR settings, enable the Advanced Settings, and under Controllers find the button “Show Old Bindings UI”
Step 4. In the new window, select your Unreal project, with the name you gave in Step 0. In my case “VirtualStudioProject”
Step 5. Under “Current Controller”, click the “Vive Controller” button, and now you should see “Vive Tracker on Camera” (This only appears after you selected a role from step 2. There will also be a regular “Vive Tracker” option, this one does not work)
Step 6. Under “Current Binding” click Edit.
Step 7. Now click the button “Edit Action Poses”
Step 8. In the new window, click the button “Unused”
Step 9. And finally, now for the part I’ve been looking for for hours: Select “Special 1”
Now it should be working again in Unreal, if you add a Motion Controller Component, and set the source to Special 1.
As you can tell, this is not intuitive at all and a huge step back from what it was.