I think split poly will do the same thing. You might have to smooth out the edge loop with average vertices or sculpt geometry tool, or just move it using normal average to get it to smooth better. Someone with more experience could probably help more (I guess it depends on the type of geometry). But essentially, adding loops with split poly or insert loop will change how it smoothses (?).
"The planning of the picture, therefore, is the all important thing, not the execution." -Max Brödel