I got the second part when the there were glass and an alum cup over the ball:
He pushed the cups towards the first guy to hold, thus he could extract the ball from underneath, then he pulled the other cups towards the second guy, so he can push the ball underneath..

And the part with the tennis balls:
Watch as he puts the cup down - first it's pointing the wall, as he puts the tennis ball inside, then he puts it on the table - same thing with the other ball - he points the cup towards the wall, not facing the crownd, and puts the ball inside, puts the cup on the table..

http://www.youtube.com/watch?v=nj6DK_WX7Yc#t=6m56s

... you can see that he puts the second tennis ball in there