I noticed that a number of the boats set up their asymetrical spinnakers so the sheets pass forward of the luff, not behind the luff. I haven't flown many asymetrical chutes but they have all sheeted behind the luff like you would do with a jib.
Sheeting forward makes a lot of sense though; nothing gets tangled and the likely hood of it running away from you on a jibe because it can luff straight forward. One drawback is it is easier for the sheets to drop in front of the bow and then go under the hull. The Volvo racers seemed to have remedied the problem by taping a short stick or even a spoon right off the tack so the lines stop on top of it.
I guess the other thing is you might need slightly longer sheets.
Any body flown an asymetrical spinnaker this way?