Rough Keys on Set

For an upcoming greenscreen shoot on HDCAM I wanted to look into some options of pulling rough keys on set to show the art director. The production company is shooting on an F-900. My plan is to have the camera record the entire shoot to tape, but at the same run HDSDI output from the camera into an ioHD which would be hooked upto a MacBook Pro. That way I could pull select setups and capture them on the fly and just do some rough comps on set with keylight in After Effects so that the art director can see how the background plates are lining up. I want to see if this is a viable option and also ensure that nothing about this would affect the in-camera recording. Also if there are other hardware solutions that people have used on set to accomplish a similar task I'd be interested in hearing them. I'm sure there are plenty of ways to accomplish this, in this case I was trying to satisfy the art director and not increase the cost of the production budget too much for the agency. Any info is appreciated. Thanks!

- Mike