First, start the Treacherous Swine mission. After you kill Gonzales and receive your wanted level, get into a vehicle. Pick up the bribe nearby. Do not head to the Pay n Spray or clear your wanted level. Now start a new game. You now have free use of the Pay n Spray!
The game's save file saves this so you can keep this ability when the game is savaed. This glitch will fix itself if you complete Cortez's mission and it doesn't carry over to other save files.
So, can someone confirm if this work for you and all versions just to see if it's not a quirk in my game?
Edited by spaceeinstein, 04 February 2010 - 07:29 PM.