fisheye - How would one use filters with the "bulb"-like shape front element lenses?

I am toying with the idea of picking up either the Samyang/Rokinon 14mm f/2.8 IF ED UMC or the 8mm f/3.5 Aspherical Fisheye lens.

These lenses have a built-in petal-shape hood and a "bulb-like" front element. I came across a few reviews about the 14mm f2.8 lens but all of which mentioned the "unusuall" front element and the if so special lens cap that should always be on the lens when not in use. At least one review says it is not possible to mount front filters on these lenses. Surely, there is a way...

In situations where I would be normally using these lenses I would want to be able to use ND filters. Is there any way to filters to these type of lenses and if so how and what type?

Answer

By default, you are unable to place filters in front of those ultra-wide angle or fisheye lenses.

There are however, 3rd party accessories designed to tackle just this issue: