You can do this.
Panda’s rendering loop has quite a few clears in it:
for all windows by window sort order do:
if win.clear_depth then clear depth buffer of entire window
if win.clear_color then clear color buffer of entire window
for all displayregion by displayregion sort order do:
cam = displayregion.camera
if cam.clear_depth then clear depth buffer of displayregion
if cam.clear_color then clear color buffer of displayregion
render camera into specified region of window
So basically, all you need to do is create a new displayregion in the window with a new camera, and set the camera to clear the depth buffer of its region.
Here’s a recent thread that shows how: