Mi dispiace, there is no "Move" verb in the ZipFile class. The metaphor or "object model" for the ZipFile class calls for applications to "Add entries" or "Add files" or "Add directories" into the ZipFile.
There is a FileSelector class that may help you. Rather than calling AddSelectedFiles, you can use the FileSelector to directly select files. With that selection of files, you can then perform 2 actions: add the files into the zip, then
later delete the files if appropriate. It would look something like this:
Dim selector as New Ionic.FileSelector("*.mo")
Dim selection as New List<Of String>
selection = selector.SelectFiles("d:\work")
Using zip As ZipFile = New ZipFile
'' Delete files in the selection here