It's not a stupid idea at all. But it might not be optimal for you for the same reason most horizontal woofer-tweeter-woofer center channel speakers aren't the best solution for center channels.

If you generally listen from the sweet spot (or within a 6 inches or so one way or the other) you should be okay. Getting off-axis 15 degrees or more can really cause some lobbing problems though, and it's likely that you'll tend to hear 1 speaker over the other, so the center would be skewed to the side closest to you. Depending of course how close to the TV the center speakers are. The result is bad sound further off axis you go.

If you don't suspect this to be a problem for you, or you don't care about people outside the sweet spot area and your amp is up to the task - it's actually not a bad way to go. I've met a few bachelors who do this very setup and swear by it.

In my honest opinion though, because of the added costs and off-axis complexities, why not just run your front mains in "phantom" center mode...It's basically the same thing, only a few hundred bucks cheaper. The off-axis problems are more obvious, but you save a ton of cash which is always a good thing IMO. 2 more speakers is a pile of money for the marginal benefit of the center channel - I'll leave it to you to decide, but just be sure it's the best place to upgrade your system.