In the FIVB rules, it says that "within the playing area, a player is not permitted to take support from a....

Question

team-mate or any structure/object in order to reach the ball." So would it be legal to for example jump off the wall to play the ball since the wall is not in the playing area?

Answer 1

Actually, if I'm not mistaken,

You CAN step on the bleachers as long as one foot remains on the playing surface (ie the gym floor). Then it's still valid.

If in a tournament where there are two courts in a gym, then you cannot cross the half way line.

Answer 2

No because you are not allowed to step out of the playing area or you are out and the play ends with an out call and a point for the other team

Answer 3

Dan is correct.

You can not use anything to help you play the ball.  You can not help a team mate hold you so that you can reach over a non playable area to play the ball.  There are dividing nets between the courts in the gym where I work.  You can not have your team mate move the net out of the way so that you can play the ball.  

In your example, you are using a non playable area surface to help you play the ball.  You can not use the bleachers or the bench to help you jump to play the ball.