Has anyone installed a larger tank (and do you have any pics or feedback on it?)

I recently picked one of these up from a flying buddy who has a K210 in it. He only gets 5 mins flying time with a small reserve of fuel and that's using a Taxi tank. He's not flying 3D or particularly pushing the throttle. I'd like to have 5 to 5.5L so I don't need a taxi tank and can have 7 mins flight time while keeping a 20-25% reserve. I was surprised to see Jettech and CM Jets don't have a bigger tank in inventory. I suppose I could fit the smoke tank and plumb them in line but I was hoping to add smoke.