Interesting thought, but probably not one that will float. His changeup is not considered fantastic. It is fantastic that as a reliever, he throws a third pitch, but his change is far from plus. He is a 2 pitch pitcher with a plus fastball and a developing curveball. His issues seem to have been staved off this season, as he had trouble with command in the zone. He is finally putting it together out of the pen, doesnt seem to have the arsenal for starting, and hasnt started a game in 3 yrs. So I'd say, not the best of ideas.
In fact, I predict that Okajima has an off yr next yr and Delcarmen will be a beast in the setup role.