Not sure if this is the one you're looking for, but there is a technique described in Matthew Usher's article on the Revell '63 Corvette in the November '05 issue.
Basically, it involves spraying paint through an extension tube attached to the spray can nozzle into an airbrush jar, with the mouth of the jar covered with masking tape (through a hole in the tape) to avoid backwash. Allow time for the propellant to dissipate from the paint in the jar (an hour or two) and it's good to go.