As Brandye pointed out, many of us have "discovered" this technique on our own.
The way I do it is a little different than as explained in the various blogs/websites.
I start off in "regular" cunnilingus position : lady on her back, gentleman's head between her legs
not at a 90 degree angle. I then use the back of my index, middle and ring finger to massage the lower part of her vulva and her perineum (my fingers never go inside her vagina). To give you an idea, the part my middle finger's middle segment that is just above the middle knuckle applies pressure on the perineum*. (for the visual folks out there, I look like I'm yawning, with my fingers covering my chin instead of my mouth. My hand is not flat over my chin, just the 3 fingers .. looks a little like this
http://dedalvs.free.fr/images/slipa/handshape/m.gif )
By massaging, I mean small circle motions. I don't do crazy movements. It's just about putting the right amount of pressure on the perineum and rubbing her labia at the same time.
What I like about this variation is that the little circling motion of the fingers spreads the lady's natural lubricant and gentleman's saliva a lil everywhere and inevitably on the perineum as well. This facilitates the massaging of the perineum (and permits a greater circling motion). The rubbing-pressure combo certainly has an edge vs. pressuring of the perineum alone.
On another note, this variation works best for me because I don't have to be at 90 degrees with my g/f's body. Gives me a better position for cunnilingus.
*(sorry for the repeating uses of "middle", it's the semantics
http://www.humanhand.com/humanhand.html )
SQ
PS: Those of you who'll try this and get tempted with anal play in the process, remember the simple rules of hygene. Your fingers should not go from the anus area and then in your woman's vagina.
Have fun