Shadowcard said it correctly with the leeway issues, however, I find that better than an official penalty is debunking their strategy by granting time extentions when I see someone stalling. If you think you are going to win it in those last 30 seconds or so, and slow play accordingly, having an extra 2 minutes added to that clock throws off your stall tactic, and if a game is close enough, can make the difference.
If my judging will be questioned because I tried to be nice by simply reminding a player that they need to hurry along, or telling them that they need to stop trying to distract their opponent, then so be it. I will start issuing officially documented penalties to start off with, rather than try to be understanding as I have done in the past. That seems to be what you are getting at.
Just because I have never documented a penalty against him for stalling does not mean that he was not verbally warned, or given time extentions by myself and other judges on NUMEROUS occasions.