Originally Posted by Yarn or Fabric

I assume you are using a die cut since they look so nicely cut out so this will probably not work... but I'm going to say it anyway...
If you could make them 1/4" bigger on all the sides, sew it right sides together with a thin possibly fusible interfacing, then cut a slit in the interfacing... snip your curves and turn it right side out. Use a chopstick or something to get your curves all nice looking. Iron it out and then you can just place it where you want it to be and sew it down.
If you are using fusible interfacing make sure you iron it on to something that it won't stick to - I keep a larger piece of that non sticky paper from heat n bond for stuff like that ;)