Did you read the first One Block Wonder book? She tells how to do it, and it works great. I've made 2 of the 45 degree OBWs by making 4 layers of the fabric for the corner pieces. The trick is to put all your kaleidoscope blocks (I used my kaleido ruler to cut both the blocks and the corners) up on the wall, and stick the corner squares in different places until they blend.
Then your need to pin the corners to the surrounding blocks, sew them on, and replace the 4 blocks on the wall. If it's a small enough piece, you can use a portable "wall" of batting, and lay it flat on a folding table near your machine.