From my dealings with these kinds of processes (twice) 90% of US immigration law is based upon your intent at the time of entry.
I've entered the US under the VWP with a single entry K-1 visa in my passport. The immigration officer wanted to know why I was doing that but a quick explanation was sufficient. As I was entering opting to not use the K-1 that was seen as being fine.
Maybe I'm supposed to read between the lines but haven't...can your friend enter the US under the VWP? If so based on my experiences I can't see why he couldn't again even with another visa in the works.
This post does not constitute legal advice...blah, blah, blah, don't sue me if your friend reads this and his life is ruined as a result of my writings 