I don't beleive this is possible simply because if the shorted shares were being offset by corresponding long posiions, these long positions would have to be reported as either institutional and/or personal holdings somewhere, just as the others show up.
Also, remember, the short position of ~150 million (135 US + 15 Canada) is almost 25-30% of the outstanding float of ~525 million shares, a large chunk of which is held by a very few!
So, assuming the top 5 institutional holders have ~ 30% of the float (and these people will not short their shares because they are genuine investors), that half of the remaining instutional holders are shorting what they hold? I doubt it very much!
Most of the ~150 million short position is a real short, and these shorts will pay thru their nose in the not too distant future!
The day these shorts decide to exit the packed auditorium when the weakest amongst them yells "Fire", the only crammed exit will not allow them to exit - especially if the fire is at the exit itself! They will roast alive!