I was told freezing a transition is not possible. The work-
around is to use a mask instead. I'm not sure what
capabilities Video Factory has in this area, but there has
been discussion on this forum addressing the issue.

Search the Vegas forums on 'hold transition' and you'll
find a message about holding transitions with some
instructions.

Short answer: you can't hold transitions, you must use a
mask, and you'll achieve the same result.