that's an interesting post, but it solves a whole different issue.
I am disappointed about the lack of DelegateControl customization support in Sandboxed solutions, because I expected that I could distribute my recently published CodePlex project (http://devdashvis.codeplex.com
/) as a Sandboxed solution. It consists of only a set of .js files that should be referenced on every page in the site collection. Unfortunately, I was forced to wrap it in a Farm solution.
I think there will be many more js-only solutions in the future, in particular because of the Client OM and REST, and they will all be affected by this limitation.