I have come up with a new fixer though. I'm calling it T-Shart!
Here's the plan:
Using a small canvas, cut the shirt so that it will overlap at the back
without too much bunching material.
Using a staple gun, attach to the back, as neatly as you can be bothered.
Hey presto! A Canvasaur!
It makes a nice addition for a kid's bedroom, keeping it cheap, making it personal, and along with the paper aeroplane bunting and the pompoms, really brightens it up at very little cost. And your creative maestros can even get stuck in!