Strobe for WP-DC300 (Canon S40) - Help

I have a Canon S40 with the Canon WP-DC300 housing. I want to add a strobe and am most strongly considering the DS-125 for the TTL operation. Because this strobe fires off the flash from the camera, if I don't do something to deflect or diffuse the camera's strobe, won't I get backscatter? If so, any suggestions on how to prevent this problem? If a different strobe set-up would be better, I'm open to any suggestions.

Thanks

I used some silver folie tape. The use it for air-channels and you can find it in most hardware stores. Just stick it on the inside of the WP-DC300 body in front of the internal flash and leave it above the strobe open so that it can reflect up to the remote sensor of the DS-125. It worked great with my old setup WP-DC100 and Canon IXUS 300.

Mike.

How do you set the camera & strobe to use the TTL operation?