well i did it,
no real attempts at an actual decent image yet, but heres something i snapped off within 15 minutes of finishing it.. 100%sooc (with exception of watermark obviously

i jumped inbetween him and his xbox game... so naturally i got a serious expression

(i hope you can see it.. its set to pirvate)
Shutterspeed:1/60
Aperture: f/9.0
Focal Length: 35 mm
ISO Speed: 100
sb600 at about 1/8th
(pumped up the flash and stopped down to give the ringflash a bit more even spread.. that was my logic anyway. i know technically i could have gotten away with a lower flash power.)
heres a shot in the mirror. it doesnt seem to be wrapping around the entire ring.. but its just a bit dodgy to dangle a second flash off the top.
i made it from a $1.50 bowl and a 1.5ltr pepsi bottle, two plastic bags and a bit of duct tape.
i covered the inside of the bowl with the greyish/silver tape as the bowl was semitranslucent, and then covered the front with about 5 layers of white plastic (you know.. supermarket bags)
the centre ring extends about an inch past the edge of the outer ring.. so at about 30mm i get edges if the pepsi bottle showing,.. but thats fine..
as you mentioned there is a little bit of play for re-composing.. not as much as i'd have liked.. but it does what i want for now.
good looking light
i'm pretty happy with the results.. my only point of ponder is the circular catchlight.
i dont relly like them.. however.. when i get closer nd the catchlight encircles the pupil... i think its pretty cool.
watch this space.. i'll make an attempt at a half decent picture and see how it looks..