Did you ever get a response or figure this out. I'm having a similar situation and would be nice to click a button to kill the output on the external...

No. The only solution I found is to purchase the pro version of DiscoBrick and syphon its and SV's output to a video mixer app like CamTwist and use that for visual output. But my 2011 iMac i5 drops more frames than I would like under this configuration.

Ya that would work with disco brick. But you need an computer with an i7, 16gb of ram, and 1gb video card or better.

I run an macpro i7 with 1gig video and ssd drive and even with serato video and other video apps running I have good framerate. I just wish serato video would have a double click option to Max and min the video output for us wedding djs that need that quick and easy transition.

Try Mix emergency it will do what you need much better.

I downloaded the demo version of mixemergency and its great, Kinda wished I didnt buy serato video cause i will probably buy m.e. since it does seem to be a bit more user friendly and easier to navigate but I guess I'm still not finding the solution I thought I'd find. It does have the double click output just fin but let me break it down:
I mostly do weddings and Family Reunions and Sweet 15s etc. Well all those events love to have a slide show going on during dinner so I have them upload pics to me and I make a video without audio, I run two 40 inch flat screens through a hdmi switchbox and basically it will output to both tvs at the same time from one laptops hdmi right, so I like to also throw in some dinner music videos once in a while so there comes the issue. If I run the slideshow video through m.e. or s.v. the video plays at the speed of the music rather than the original speed. If I stop the platter the video stops, so I need to play the video though a separate program so it doesn't get manipulated by the sound but when i want to throw in a music video I want it to look professional and not have a mouse cursur scrolling over to move the slideshow off and pop up the music video visa versa. I guess I could use quicktime and hotkeys to output the video and then use M.E. to output the music videos by double clicking the preview window when i want it to scroll over to the tvs. It would not be as smooth as a fade but it beats a mouse cursor. I think i might have just answered my own question, unless you have another suggestion. Also, M.E. has been running about 2 hours in demo, i just keep restarting it as i learn it and play and the mac is hotter than it's ever been...even using serato video all night it hasn't gotten this hot, I'm not worried cause i know the fans are working and i have a cooler under it as well but do you suggest manipulation of the automatic fans to bump them up to higher rpms so the laptop will stay cooler longer at a gig? I've read all the ups and downs but always looking for input. Sorry for the book but thanks for the replies.

Have you tried Radikarl's free slideshow quartz composition: www.radikarl.de It would eliminate your need to make a video. You just drop some images in a folder and it will run a slideshow. I used it for the first time last night and it was great.

I even automated it a bit by using an online cloud storage sync like Dropbox. I used box.com because they allow uploads by email. So, the crowd sends their pics by email which syncs to my slideshow folder on the PC. Of course you could sync it to a different folder first so you could preview and filter inappropriate pics before dropping them in the slideshow folder.

You can run ME in standalone mode, unrelated to the music or decks playing