engine - 8:49 am on Jun 5, 2013 (gmt 0)
Welcome to WebmasterWorld
You're not alone in this. Duplicate content on the same site is a bigger problem.
Are you sure the distributors don't already know about the other brand? Since the Internet, this has been a bigger problem to get over. In the past, you'd print brochures, which look different.
At the very least, your sites should look completely different: The UI has to be significantly different.
The real way round it is, as you indicated, creating different content.
Crazy idea: Even so, if it's only the distributors that use it, why not consider the site for distributors is not indexed at all in the search engines. Add your own internal search to that site. Keep the site that sells direct as the only one that is indexed.