I tried my neighbors kneely chair with my cocktail, and, 
while it was a bit unconventional it was also very comfortable/ergonomic.  
I played through a few games on it.  
I didn't have room for it, though; so now I straddle my 6 liter bucket that I also use for changing aquarium water. 
  
BTW...not even kneely chairs can save gamers from numb-butt.