Sima made a 100mm plastic lens in a plastic tube with a T mount. You can mount it on any 35mm body that you can find a T mount adapter for so should be able to find a way to fit it to the EOS. They sold in the 1980's so may be inexpensive if you can find one. Focus is push/pull instead of a helicoid and aperture is a set of disks with holes.
You get the toy camera soft focus but not the vignetting. The softness varies with changes in aperture. For a sample of the effect see
this article on photo.net.
Martin