Actually, it's pretty easy to add these to a texture polygon, I've done this with webcams, although to get any reasonable efficiency you need to make a separate collada object for each timestep.

I did a quick test of this with four webcams and a conference room, in which our server automatically generates a kml files and a series of .dae and .jpg files for putting each webcam's image on a wall. Here's a screenshot:

http://www.kaszeta.org/rich/download/conf_room.jpg

(If I can get this converted to use external urls instead of internal ones, I'll post a link for it)