I've never put a quilt block onto a t-shirt, but I did put one on my favorite sweatshirt...after I dropped some lunch on the front & couldn't get the stain out! lol I had an extra block from a guild swap-a-block & just pinned it on & sewed around the edges. Even managed to get it straight some how! :D Of course, a sweatshirt does have more "body" to it, so I think a stabilizer would be needed for a tee. Then again, if you used fusible, like Steam-A-Seam2, that might be all the stabilization you would need, then just do a zig-zag around the outside.
I've also been thinking (and YES, it did hurt!) about making a quilt out of all my stained tees - the "Stained Shirt" quilt! That's what happens when you're a Gemini & can't just do one thing at a time! lol And it usually happens at home - here at work I actually have a big flour-sack type dish towel that I clip around my neck when I eat lunch at my desk. :wink: