I've worked on a design of my own, but I'm glad this product has come out, will have to try it.
For my own design I started with a
water polo head/ear cover as a base on which to build. Water polo head covers use a nylon mesh (covering most of your head) on which is mounted two plastic cups which protect your ears from the impact of a water polo ball. You can modify these things to your hearts content and come up with your own design. Just wear your bike helmet over your creation.
Another element you could add to the design is a section of parabolic dish covering each ear, facing backwards (dish could be salvaged from a lamp or speaker etc). This would protect from the onrush of wind from the front, while simultaneously reflecting noise from behind your (such as cars, other riders, etc.)
Also think about the ears of animals, such as the Canadian lynx, which have hairs covering the edges of the ears, as the edges create turbulence hence noise, and the hairs breaks up the turbulence. This element does not appear to be present in the Slip. Perhaps the designers thought it too silly for the market, heh, and probably right.
Also check out the patent database at
www.uspto.gov, as I recall finding perhaps a dozen related patents from decades past, all expired.
Have fun!