I don't have any real evidence for this, but I suspect that the film makers suspended the bike and rider from a helicopter and simply lifted it over the gap. If that was done, there might not have been a human rider at all, but if there was and he was properly secured it would have been quite a safe stunt.
This would make it a little like the celebrated (although rather more modest!) Harley-Davidson jump in Terminator 2, for which there's a description here.
The helicopter could have created the parabola effect of the jump by flying an equivalent path, or it could have flown straight and level and used a winch system to adjust the altitude of the bike.
The only computer enhancement necessary then would have been to digitally erase the cable(s) attached to the bike, which is of course a very commonly-used modern technique for all kinds of stunt work.
Looking at the video on the behind-the-scenes page, the editing style means the shots are very short and it would have been quite easy to disguise any artificiality. In support of my hypothesis, there is also a shot of a bike suspended from a helicopter on that page, although in that case the purpose might only have been to lift the bike to otherwise-inaccessible higher ground.
All of this of course assumes they didn't just render the whole bike and rider using CGI - it's possible! :)