You could put a command button on your form that creates a new item using the same form and copies data from one item to the other. To create a new instance of a custom form programmatically, use the Add method on the target folder's Items collection:

   Set newItem = targetFolder.Items.Add("IPM.Post.YourFormName")

If it's a message form, use the Drafts folder as the target. If the target is a default folder, you can use the Namespace.GetDefaultFolder method to return it as a MAPIFolder object. To create an item in another person's mailbox, use Namespace.GetSharedDefaultFolder to get the MAPIFolder Otherwise, you can use the code at http://www.outlookcode.com/d/code/getfolder.htm to walk the folder hierarchy and return the MAPIFolder corresponding to a given path string.

See http://www.outlookcode.com/article.aspx?ID=38 if you need help with property syntax.