Im actually working on this idea as well. It is possible. I wouldnt so much call it 'ripping off the Havoc engine', I would call it utilizing the fantastic Newton engine. Who needs Havoc if you have a viable, free physios engine supported by a really nice and intellegent guy (Newton)?

In thinking about how to achieve this effect, my only real concern is how to transistion the model from its normal, animated mode into a prearranged 'ragdoll' pose. I'm pretty new to c-script, though, so theres probably a method im overlooking. Perhaps through the bones system, an entity can be quickly posed into a 'spread eagle' sort've position before being switched with the ragdoll (which would also be in the same position).