I don't know about Vegas doing this directly but perhaps the deck will help you out. I'd check to see if the deck has the ability to restripe the audio. Well thinking about it some more the deck will have to play the right tune anyway else it's going to record something over the video.
I don't have a DigiBeta deck here to check but I'm 90% certain it's doable. Question might also be if in that mode the decks will accept embedded audio or if it needs AES or analogue.
Bob.