Screencast video with trainer narrated video inset

Hi

I'll be recording some live classroom training sessions with a trainer using a laptop displaying slides and software demos. I'd like to produce a screencast with the trainer video headshot being shown in a small box in the corner (or to the side). (Possibly moving the box when it covers some important aspect of the screen).

I plan to record the laptop screen with Camtasia, record the trainer with a video camera using a wireless tie clip mic and then composite the trainer video and screencast in Camtasia afterwards, rendering to 1024 x 800 pix.

Does this sound do-able? Anyone have any suggestions as to a better/easier way. It did occur to me to use a webcam image floating over the screen but the trainer will be moving around the room when delivering the slides and answering questions etc.

Any ideas gratefully received.

Thanks