Muzzie's mehtod will be easiest probably. Add a "~+Amovie1" and then you can toggle the video on and off. You can also add "~-0movie1" through "~-9movie1" to have an two sets of frames--one "off" and one "on".
SlayerWraith did a nice example using env_renders...but he's since deleted it. Maybe if you PM him, he'll send it to you.
3DMike did this too on his cs_bikini map, but I'm not exactly sure how he did it. You could drop him an email and ask, or decompile lol.