There is a trend in Japan to pop up the camera's internal flash for simple macro shots that is becoming popular. I have done some testing, and this technique forces me to use higher iso or more open f-stops than I'm comfortable with, but can see the attraction for a compact, easy to use setup.
Seatool's 40d housing is built this way.
Seatool Housing for the Canon 40D with Pickup Viewfinder [st.40d.pu] - $3,199.00 : Reef Photo & Video!, The Underwater Photo Pros