You might be able to mask off and paint your pinstripes. They sell masking tape that has a removable strip or strips. You lay one piece of tape, then pull out the removable strip leaving you with a uniform space between two strips of masking tape. Paint the stripe, then pull off the masking tape. Here's one brand and you can see the 'resulting painted lines'. Finesse Pinstriping Inc. - FinessePinstriping.com
Different tapes would give you options like two parallel stripes of equal or unequal width.