Change his name to William J Wright, although the first name can be interchanged with some other judeo-christian name, which isn't hard I know. Whatever, just roll with it for now. Change the setting to California, make that the state where L does his broadcast and narrows down his investigation. Also, L sounds pretty dumb when you try to say it with a straight face, so change it to "Agent L", and we can have the two titles interchange depending on the scene and context. A lot of manga content will have to be cut out obviously, but the movie will revolve around Kira vs L. We can do without the shinigami, honestly for the most part they are irrevelent or serve as stupid comic relief. The 'Kira' title can stay, its rolls well and serves as a good title for the mysterious supernatural villain, plus its not an english word so it won't sound stupid.
Fuck I should write this.