Jonno said:
Does Vegas allow you to create a gradiented (graded? gradaded...?) mask?

I think a slightly 'windowboxed' effect, with a soft vignetted edge around all four sides could be very effective method in masking those distortions, with the extra benefit of evoking that lovely 'projected' look.

I don't know Vegas very well at all, but we do have it running on some edit suites where I work, so I could have a poke around the masking options and get an idea of what's possible...

Yes, you could add a feathered mask in Vegas (or really any editor for that matter). It would simply involve making a .PNG the appropriate size and adding it as a layer over the video in Vegas. I have done this myself for something different.