I had a similar requirement when a client needs a desktop to display the "path" of an element, rather than its name. The problem was that many of their items have the same name, which makes it difficult to distinguish between elements.
Unfortunately, this change required us to create a custom implementation of the Sitecore WorkboxForm class. I usually do not recommend modifying Sitecore like this, but for something as important as Workbox, it can be a hassle.
Locate the following file in the root directory of your Sitecore:
\sitecore\shell\Applications\Workbox\Workbox.xml
Modify CodeBeside to point to a custom implementation of the WorkboxForm class. The default class is in the Sitecore.Shell.Applications.Workbox.WorkboxForm namespace in the Sitecore.Client assembly. You can essentially open the Sitecore class in Reflector and copy everything into your new class.
In the CreateItem () private method, change the following line to use the item title (I used item.Paths.ContentPath):
webControl["Header"] = item["Your Title"];