I'm not convinced you could crimp it enough to stem the flow. From what I understand there is a lot of pressure forcing the oil and gas out. I think the only time it will be capped properly is when the relief well is drilled and operational. Once the pressure is off they can stem any flow and concrete permanently.
The new LMRP cap will be a machined flanged joint from what I understand, even that won't seal it completely if works as expected.
Looks quite mundane really...
http://www.bp.com/liveassets/bp_interne ... tream.html
Even I laughed when I heard what the Topkill plan was, but it is a little more complicated than just mud which the media said it was. Having said that it was shite.
Unfortunately it would appear they rely on the one safety cut off valve. Maybe a backup would have been a good idea.