Even when Lukaku was there at the beginning of the season they were trying to bring in another forward (Rooney) to strengthen their squad. Costa isn't anything to do with Lukaku. He's Eto replacement. It really is that simple.
I think its as clear as day that Lukaku is about as welcome as a fart in a spacesuit at stamford bridge.
http://www.telegraph.co.uk/sport/fo...t-say-why-hes-at-Everton-and-not-Chelsea.html