We put out an article in the TechNet Wiki and the code for a sample shape in the TechNet Gallery for creating a custom shape for the Visio Management Pack Designer. My apologies for the delay on this since I showed a preview of this way back at MMS in April. Since the VMPD has been beta though, we had not finalized the interface for custom shapes. It turns out that there were some changes made that broke that sample. They were good changes though since it’s much easier to install that custom shape on a workstation. The example I showed at MMS required you to register your DLL in the GAC, while we now just need to copy it to a particular folder.
If you are interested in creating a custom shape for the VMPD then this should be all you need. We are planning on creating a project on CodePlex in the near future to collaborate on some custom shapes. The idea is to give you a base starting point for your own requirements in addition to giving you access to some custom shapes that you can use for your own management packs.
As always, please contact me at MPAuthor@microsoft.com if you have any suggestions on how we can improve your access to content that you need. I would also like to hear about custom shapes for the VMPD that you think would be valuable since those could form the base of a sample project.