How about asking the people whose name are on the patent to document their work?
That said, it's entirely possible that they also developed this independently from his work. That email from the VP sounds a lot to me like "thanks for the suggestion, we already had the idea and we're working on it". It does happen to me that people come with a grand new suggestion, and it can take quite a bit to convince them that we are already implementing it, no we don't need their design doc, and please don't take credit for it.
Biting the hand that feeds IT
