Dear Mphelt,
Please take into consideration that the user interface customisation possibilities supported by the Revit API are intentionally rather limited, in order to enforce a certain consistency across the default built-in UI and additional functionality provided by add-ins.
Therefore, you need to provide an extremely compelling reason for anything to be added.
Please explain in detail exactly what you are trying to achieve and why it canot be achieved in any other manner.
Maybe the easiest way for you to move forward will be to implement your own modal dialog within your own external command, in which you can implement your own user interface making use of the full range of possibilities offered by the .NET API.
A slightly more complex and powerful approach would be to implement a modeless form and user interface, again making full use of all .NET functionality, and communicate with your Revit add-in via external events, as demonstrated by the Revit SDK
ModelessForm_ExternalEvent sample.
Best regards,
Jeremy