Right, here's what you do. Get the clip you want to edit. Make sure it's 25fps ('cos 40 ms is what you want, obviously). Split the clip where you want to insert the single frame. Take the end of the first half or the beginning of the second half of the original clip and remove one frame. Insert a still photo (make sure it's the same dimensions or at least the same aspect ratio).
Drag that photo into the timeline (make sure you select clip view, not time view). Right click on that photo, select Show Info..., then change duration to 0:00:01.
I hope you can follow that.