penalizing players not in the field of play

[mkottke]

There is another thread about a player in touch knocking the ball back that brought up an interesting point.

if he hadn't started he was an a*******le. Min YC.

I personally think that this YC is not a stern enough message and/or result. Although, my response in the other thread makes me look like an egomanic on a huge power trip.
How would you handle this situation fairly and without being an asshat?

ONON-
Mark

 

[Davet]

If a player who was on the subs bench came onto the filed of play and interfered with the game then I would red card him.

If it were the coach or a spectator then I would insist on their ejection from the playing enclosure.