Motion Tracking an object that goes off screen?

Thoght I saw someone in a tutorial adjust the track marker location using a key modifier.  Then I found this: http://vfxhaiku.com/2011/12/how-to-track-an-object-that-goes-off-scree n-with-adobe-after-effects/

And down the bottom of the comments someone said this:

"D.S. Says:

July 6th, 2012 at 5:31 am

There is a trick in AE, so you dont have to guess after the tracking.
Hold the alt/option key, while dragging to the new trackmark. AE knows automaticly that you choose a new one and makes a seamless track."

I can't get this to work. Does anyone know the correct way to do this?

Thank you!