I'm not aware of a way of directly getting the VI reference from the subpanel control after a VI has been inserted into it. Seems like an oversight to me if it's not there. This means you will either have to create a mechanism for saving the reference that's currently open at the time that you invoke the "Insert VI" method, or you can use a roundabout means like getting the run state of a VI or reading an indicator's value, as mentioned in this thread.