The Catherine Palace is definitely worth it, so is Pavlosk [I prefer the latter]. Gatchina is not all that cheerful and has been woefully neglected, but restoration is ongoing and I enjoyed it. The village itself is lovely. Not as much of "tourist town" as Tsarskoye Tselo.
Another good visit is Peterhoff, but besides the magnificent palace and it's parks, the recently restored Island pavilions are worth the little extra effort. And, a few miles down the road, another neglected treasure- Oranienbaum. Ignored by most tourists but the park is very popular with Russians.
I hope your boss has a personal guide and driver, not a tour bus thing.
I am now planning personal tour for a friend of mine. I advised against going in the summer, the crowds are unbearable as well as the mosquitos, but that is the only time he has. To avoid as much of both as possible, I am suggesting the above places to visit as well as the "must sees".