I posted a VI which does this in this thread, but as you said, the attachments are missing. You can use the report to a moderator button on the post to ask the moderator to find the function. I also posted a document in that thread (reply 21) which shows the various plugin overrides you can use.
I can't look at either of them at the moment, but if memory serves, the conpane for the VI is the 4-2-2-4 pane with an I32 output wired to the top-right corner. I believe it should be 1 if you want to cancel the creation of a new VI or 0 if you want to allow it (or the other way around, or it might have been 1 and 2).