Sony's unique speedlight design requires a different approach when it comes to flash diffusers and bouncing.  To that end, Gary Fong has developed the Gamma Diffuser for the Sony HVL-F58AM and HVL-F43AM speedlights.

There's a brief intro in the following video if you can get past the rather poor audio, the design makes sense in terms of its functionality and performance.

It's currently available for $30 from Adorama and Gary Fong's website.