Straight from the manufacturer ... no guessing.
I wrote Gary Fong, Inc., to see what they product they would suggest, after I submitted an image to them of the SONY HVL-F58AM Flash.
Here is the response:
"Below is the answer to the question you recently sent to the Gary Fong, Inc. Support Team. If this response does not answer your question please use the link to update your question so we can take another look into this incident for you.
Summary: Using FONG products in concert with the new SONY HVL-F58AM Flash
Created: 12/9/2008 12:45:45 AM
Updated: 12/9/2008 11:50:07 AM
Robbie - Gary Fong Support 12/9/2008 11:50:07 AM
Thanks for writing and providing a reference image.
As a matter of fact, the Lightsphere will still work with this design of pivoting. The surface area of the Lightsphere is practically the same whether your flash head is turned perpendicular or parallel to your subject. The reason Gary suggests turning the flash initially is so you can easily transition to vertical / portrait mode from a horizontal / landscape. The inside texture of the Lightsphere is what refracts and disperses light evenly. As long as you have the flash head pointing "up" towards the ceiling, the diffuser will still work effectively.
If you have further questions, please us know.
So there you have it ... an official reply. ;)