I happened to see an accounting professor from Detroit's Wayne State University this morning so I naturally took advantage of the situation to ask him his thoughts on accounting for emission credits. He reached the same conclusion I did in my earlier post on the subject - there isn't really a way under current generally accepted accounting principles.
One possible way to do so would be to recognize some kind of a deferred revenue/liability that would offset the value of the credits, but that doesn't accomplish much. The professor also brought up that the credit may only have value based on future events. He recognized that this result is a shortcoming of the current accounting model.