On the 1DS3, your can turn on the highlight warning blinker. But it turns it on for both the "info" view with the histograms, and the regular full screen preview.

Is there anyway to turn it off in the full screen preview mode, but leave it in the info/histogram mode?

Can I ask why you would want to do that?

The only thing the rear LCD is good for IMO is for viewing the histogram and checking for blown highlights via the flashing warning.

Viewing the shot on the LCD is otherwise useless.

I can tell you how it is on the 40D. 1Ds3 is probably the same.
From the histogram window the first push on the + (magnification) button brings up a "fit-to-screen" display that is without blinkies.

Ahhh thanks. I'll try that. The reason I want to have the highlight warning blink on the histogram , but not on the main full sized LCD is because once I get something dialed in, I like to view the comp on the full screen. The constant blinking annoys me. Also, sometimes clients like to see the LCD screen--because their point and shoots have it and it's Pavlovian.

Anyway, thanks for the tip on the +.