Okay, I work for a dealership, and it's time to let you in on a SAD SAD fact... for a non-turbo Mitsubishi Lancer 1.5 litre, say CE 96-2003 model, manufacturer specifications for oil consumption, normal oil consumption i believe is approx. 600ml per 1000km. Therefore at a normal supplementary service interval of 7500km, your car could use 4.5 litres of oil. Last time I checked thats less than what a 1.5 Lancer holds.
There's always a loophole. If you go about it the right way though, you will get what you want, if of course it's not glaringly obvious there is a reason (like a leak, or a modded engine)
I'd hate to see what normal consumption specs are for a turbo engine.
Could it be the turbo leaking oil? Not necessarily rings... Could be valve stem seals. Either way, if it's getting towards end of warranty, try your best, do what you can, but make sure you have the right answers. If you bought the car second hand, they will probably say that the previous owner must have thrashed it. What can you say to that???? Not much.

Anyway, sorry to be the bearer of bad news... Good Luck, i hope it works out for you.