desk for lounge chair arm? Answered

Looking for a way to mount a small desktop to a lounge chair arm WITHOUT altering the chair.  Have seen things like this...

http://www.amazon.com/Smartworks-Pocket-Sofa-Couch-Organizer/dp/B0032JSF4O

...but prefer something a little larger, like the tablet desks you find on lecture hall seats.  Any ideas?  Or if you've come across an Instructable to that effect, please post a link.  Thanks!