I've been working on a variation of this for almost a year, and I've found it VERY humbling!  It's really been like starting over--humbling and frustrating--a true gumption trap. The whole routine is at the direction of my teacher, Rolla Durham, whose patience is remarkable, to say the least.

Breathing on four, I buzz low C on one, and hold for 2 beats.  Then I breathe on 4 again (in what would be measure 2 of this cycle), this time playing the low C softly, with a tongue release--softly, but not tentatively.  I do this chromatically up to middle C (3d space).  Then I add the lower two octaves, buzzing then playing--that is: buzz middle C, play middle C; buzz low C, play low C; buzz pedal C, play pedal C. Continue up chromatically.  Once I hit 4th space E, I try to add the lowest pedal E to the mix.  I continue up to high C.  Thinking of  articulating using front-rounded vowels helps me shape the embouchure for proper support.  There's other stuff I think about in doing this, but these are the main points.  As Chase points out, doing this softly is the key.

In most of my playing experience, I've never needed to be a quiet player. Volume or strength were what was most needed.  I never developed this type of control, so after 28 years, I'm learning a better way to play.  Progress seems slow, although I've started to achieve a consistency in the quality and security of attacks using this method, and slowly but surely, this exercise is paying off in terms of my strength, endurance and sound, even on my rock band gig.  It's given me confidence to approach classical music, which I always thought was unattainable for me due to the requisite finesse and control--this Easter, I played my first brass quintet gig ever, at the age of 40.  I'm a ways from mastering this exercise, but I've come a long ways with it in 10 months.  With continued practice on this and everything else, I feel I can be a much better player than I ever thought possible.
Learning to develop this feel has been an epiphany (albeit a slow one!) for me.  Now, I'm finally getting what it means to think of whistling (ala Clyde Hunt), or focusing the embouchere as opposed to playing flat against the face.  By the by, it has also increased my range, even though I'm not working specifically on range.  This is not the only thing I work on in lessons, but I feel it is key in my progress on trumpet.

Giz