just scratch off, and paint! thats how elmo does it!
That was... cute? NEXT PLEASE!
The enamel on the case itself is thinner then a standard 11"x 8 1/2" piece of paper as a rule. Using a super fine sand paper to gently and evenly give the surface an abrasive feel while still being even across was the better idea that proceeded that.
The hardest part will be the actual spraying more then anything. You will have to go evenly back and forth with a continuous spray. You don't want end up with ripples in the finish from uneven saturation.