This can definitely be done, but would be all custom coded. I assume that by "structured Help content" you're referring to the source XML for your Help? Help is frequently delivered as HTML (or XHTML), as opposed to the actual XML source being delivered .. but either can be done. Regardless, your application could be coded to read this XML model and display the content of certain elements as UI strings. Really fairly simple as long as you can get your application developers to go along with the plan.
One application that comes to mind that has doen this is called WinAnt, developed by Tony Self at Hyperwrite. This is a GUI front end to the Ant build process for the DITA Open Toolkit. The strings in the application interface are all pulled from some underlying DITA files (I believe). Here's some info on WinAnt .. http://www.hyperwrite.com/Articles/showarticle.aspx?id=71
Actually *how* to do this will be largely dependent on the platform and underlying language that your application is written in .. and it probably more that people could go into in a forum posting. If you need detailed assistance .. I'd be happy to work with you on this (see contact info below).