It's very easy to handle a Javascript fallback for Slider.js: Instead of having an empty container in which your slider will be templated, put the content for the non-javascript into it.

That's it ;) Just because the Slider Javascript will empty the content of it ;)

(Side thought: maybe I'm wrong, but in 2011, are we still need a JS backwards?)

1) Your website requires backwards compatibility

2) It's not his problem

Better whine and complain on the internet until someone fixes your problems for you.