Nick from SharePointNick.com has done it! Check out the article he posted about writing back to the datasource using the BDC at Business Data Catalog Read and Write- You got it!
Grab your copy of the BDC Meta Man here
We've been working on BDC Meta Man for little over a year now. Along with the first release I think the feature I can show you today is just as exciting! I've always known that being able to write back to a business data catalog source was possible, but finding the time to create the new functionality was the reason for it taking so long. I also wasn't 100% sure that Microsoft would want us to make the BDC 'writeable' as in most presentations I'd seen they always say it's a read-only solution. Well if you dig into the SDK it is possible to find that they don't mind it being a write back solution..