How many times have you eaten a Big Mac and thought, "I wish I could justify consuming these 34 grams of fat by knowing I was simultaneously contributing to my kid's college fund"?

We haven't, either. But now you can indulge in such rationalization by signing up for a college-savings rewards program, such as Upromise, EdExpress, or BabyMint. Purchases from all kinds of retailers and service providers -- such as Borders, Starbucks, America Online, Century 21, General Motors, and Verizon Wireless -- can result in up to 25% of the purchase price being rebated in a 529 plan.

Generally, you can reap these rewards in the following ways:

  • Register your credit card, and your purchases will be monitored for patronage of participating companies. (Yes, this raises privacy issues, which you'll have to research and reconcile before signing up.)

  • Sign up for a special credit card issued by an affiliate, and you can rack up college savings as you would airline miles.

  • Use the special discount card issued by grocery stores and drugstores, such as CVS.

  • Visit the program's website and shop partner retailers.

  • Use special coupons at bricks-and-mortar stores.

  • Use partners' services, such as long-distance phone service or Internet connectivity.

Your relatives can also enroll for the benefit of you or your kids. And even if you don't have kids yet but plan to, you can set up an account for yourself and transfer the assets after you've reproduced.

If you're interested, you'll have to do some research. Not each program offers all of the above-mentioned rebate avenues, and each program has a different way of getting the money back to you. Basically, the money ends up in a college savings account, such as a 529 savings plan or a Coverdell Education Savings Account, but your choice of account differs among the programs.

To learn more -- including which thousands of restaurants and retailers participate -- visit Upromise.com, BabyMint.com, and EdExpress.com. Used conscientiously, these programs can be great opportunities to turn day-to-day spending into free tuition.

If you have experiences with these programs, we'd love to hear about them on the Paying for College discussion board, or email robertb@fool.com.

To learn about Coverdell ESAs, 529 savings plans, and other ways to put Junior through Yale, visit our College Savings Center. Also, check out our new book, The Motley Fool Guide to Paying for School: How to Cover Education Costs From K to Ph.D.