High Dynamic Range HD-DSLR Video

I was really excited when I saw that the fine people at Magic Lantern had made HDR video possible on Canon DSLR cameras.  Then I was greatly disappointed when I realized that that Magic Lantern still has no support for the Canon 7D.  Sometimes I wonder if I should buy a second camera body for those times when a two camera shoot is better.  If so I'd probably go for the T3i which is supported.  That would give me access to HDR video at a pretty low price.  How do they do it?  Every other frame is recorded at a different ISO settings.  One is darker and the other is lighter.  The adjacent frames are interpolated to come up with frames that have higher dynamic range than a single ISO setting can muster.  It really takes the hot sections of the frame and brings them down so detail is not lost.  Check out the video below.