I am not sure why a "buy-side" firm would even care about whether or not you had a Series 7 license. Besides, if you left Wells Fargo for the "buy-side" firm, you wouldn't be able to register your license with them, cause they are not a "broker-dealer". Moreover, your license would expire after 2 years if you didn't find a place to "hang" it.
You can take the Series 63 as an independent, and without sponsorship. It is a 90 minute exam, that is full of legal mumbo-jumbo, written by attorneys, for attorneys. It has very little to do with the Series 7, or the financial markets for that matter.
Some "buy-side" firms like their employees having the 63.
For what it's worth, you can also take the Series 3 ( commodity futures ) as an independent, and without sponsorship. However, you do have to register with the National Futures Association as a CTA - Commodity Trading Advisor, and that requires $100.00 per year.