I don't see how this is a 'win-win'. You say it cheapens the design if it includes a link to the designer, but then you're including a link anyway and just putting it inside of a
The only difference between inserting a backlink in a
noscript tag and hiding backlinks using CSS is that with
noscript it'll actually be seen by a small percentage of users. In both cases, you're basically spamdexing, which is no better than keyword stuffing.
Compare that with unsurreptitiously putting a tasteful credit to yourself (preferably with an appropriate
nofollow since this isn't an organically generated external backlink) in the footer, where the client has agreed to this and knows exactly how it will look to their end users. It's not deceptive to the client or search engines, and since you know everyone will see it, you'll take more care to make it look nice.
If you want your self-link to be less prominently displayed, then give it a more demure/toned down look that blends in with the design. Maybe make it smaller, or leave out any text and just put a faint silhouette of your logo in the corner. Alternatively, you could ask the client to include you on a links/partners page if they have one, or just give you a shoutout on their blog or twitter.
noscript for what it was designed for—to display alternate content to users who can't process JS.