Sorry if this is a bit vague, but I only did it when messing around, whilst Carlisle Slapper was trying what eventually became Darkest Cloud.
It goes something like: hands in crimps on the crack/rail under the roof, feet under, right hand up to good crimp on rail up and right, right heel up (i think?), left hand up to sloper on lip left of the good rail, switch heels (left heel near left hand), bump up left hand until your holding the top edge of the boulder, mantel.
That may not be exact, but I hope it helps.
