Ground Plane Manipulation

Trying to use AE2Blend to get my tracking info into Blender. I am 3D tracking a simple pan shot. However the ground is not in shot. How do I set the ground plane when the auto detector only sees a flat wall facing camera and no floor? Can I manually set the ground plane or change its rotation and set by eye?

How do you set the ground plane without ground in the tracking shot?? Thank you.