Now this thread really could be in the 3d printing forum but I chose to put it here.
I am absolutely going to give these a try as soon as possible. Macro extension tubes for the Cannon EOS mount:
www.printables.com
There is also this reverse lens adapter that uses the 18-55 and the telephoto kit lens together:
www.printables.com
I have in the past printed a microscope adapter similar to this one with great results:
www.printables.com
I recommend using a black plastic for the prints so you don't have light leakage. If you do you have light glowing through the plastic you can wrap it with opaque electrical tape to block it and it give it a nice squishy grip.
I am absolutely going to give these a try as soon as possible. Macro extension tubes for the Cannon EOS mount:
Macro Tubes by Dingolingo | Download free STL model | Printables.com
3D Print your Macro Photography - Macro Tubes In Brief Use this kit to create great macro photographs with your… | Download free 3D printable STL models

There is also this reverse lens adapter that uses the 18-55 and the telephoto kit lens together:
Reverse lens adaptor for macro photography by Dingolingo | Download free STL model | Printables.com
3D Print your Macro Photography In Brief This adaptor allows you to take macro photographs with Canon EF or EFS… | Download free 3D printable STL models

I have in the past printed a microscope adapter similar to this one with great results:
DSLR Camera to 24mm ID tube - microscope adapter by mikeeg | Download free STL model | Printables.com
This adapter mounts as a lens to the Canon EOS (Rebel, etc). The tube end has an ID of 24mm, which slips over a… | Download free 3D printable STL models

I recommend using a black plastic for the prints so you don't have light leakage. If you do you have light glowing through the plastic you can wrap it with opaque electrical tape to block it and it give it a nice squishy grip.