You are talking about locking out the center diff not the rear. Haldex functions as the center diff in this awd system and happens to be in the rear. There is no purchasable performance controller yet although there's apparently one in development which will probably never get finished tbh. There are people out there who have made they're own controllers with arduinos. There's a guy over on the C30crew forum, Jamatron I think, that has done it but he's keeping quiet because he wants to turn it into a sell-able product one day.