How to get more people to donate blood

Here's an idea. How to get more people to donate blood? Give them something in return!
Like what? How about complimentary STD testing?
Last time I called around, it was difficult to find free STD testing. Even Planned Parenthood wasn't free unless you were showing active symptoms. After lots of effort, I found one place that was inexpensive ($20 I think it was,) but it was inconvenient, requiring an appointment, and it was in an inconvenient part of town. Therefore, I never did it, choosing to rely on my tried-and-true "fingers crossed method."
So think about it: What if there were convenient, all-over-the-city, no-appointment-required centers for STD testing that doubled as blood banks? You'd be motivated to give blood way more frequently because you'd be getting something out of the deal. The converse is true too; you'd be motivated to be tested more because you'd be giving back —— this would motivate the people who would otherwise not get tested because "I'm pretty sure I don't have anything." You know, for that latter group (which includes myself), it's annoying to waste my time and someone else's time, when you're darn sure you don't need to be there to begin with. However, if your time and effort actually was helping out, you'd be way more likely to do it.
Of course, the convenience factor is the most important, so you can pop in whenever you have a moment without an appointment.
What great idea. But how would it be possible to implement this? We're dealing with monolithic bureaucracies, like our healthcare system, which are only deteriorating over time. I can only imagine something as simple and effective as this existing in a free market system.