I applaud the creativity and effort, this is not a bad idea at all, so more power to you. However in all fairness, the only way you can be 100% certain you are contributing to your candidate is to buy "official" merchandise.
Ron Paul will likely benefit more from your $18 and one person wearing a shirt rather than $0 and 6 people wearing shirts.
My solution, buy one of your cool shirts, than wear it while spending $20 on other official Ron Paul stuff like fliers.