Most part of this issue has been covered, but what needs to be stressed is this:
It can be done, but it's hard and it is likely to be broken by any update whatsapp will push out. That makes maintaining it annoyingly and undoable hard. Also, legally you can't hold it, whatsapp will requests takedown of your app in the playstore if you pull these tricks.
On the issue from Patricio, proposing a more general VNC-like approach: this would be a wise choice to implement in a new, different application, not airdroid. Airdroid chose another architectural stance. Though debatable, they chose their way and it would be weird for only this issue to implement the whole vnc-thing.