I have used TCC for many years and it became painfully obvious that the CAM version would not move into the 3d world so I have moved on to Alibre with the CAM option. I do not remeber ever seeing the ability to place tabs in a direct fashion. I think you could probably work around it by doing multiple operations. You have to understand that TCC is 2 1/2D only and will not work on a 3d object.
The post is configurable by the user but they may have a post that is already set for the shopbot. I do not know as I only used the Mach3 post.
Another option for you to consider is MeshCam. This will accept an STL model from turbocad and you can ad support tabs to it in Meshcam.
Hope this helps.