That would take a long stretch to try to turn it into a interstate or federal felony charge. They would really want to make an example, and even then, it's a pretty dubious charge to a judge.
Another way to "launder" your hobby purchases is to buy gift cards a little at a time each time you go shopping (fifty bucks or so at a time), then turn around and sell them on eBay and build your Paypal account, and then just use your ATM card to access the Paypal funds whenever you need them for a session. The bids usually fall about just shy of the value of the card, and then you have transaction fees. . .but still less than 15% off and you are going to lose those funds in cash advance fees or activation fees for pre-paids.
Even better, find a niche market where you can buy a product wholesale and turn around and sell it on eBay. For instance, I often buy and sell coins on eBay, not because I like coin collecting, but rather it is a good way to have a hobby that hides your real hobby.