These guys may have what you're looking for
http://www.rcsmoke.com/ . I've seen them used and they're usually ignited before the flight but they do have a device for igniting it in flight that is controlled by RC. Remote ignition requires a simple RC system and a 9V battery.
There are other sources but this is the first one that I came across when I searched and I think it's the one that I've seen used.
I used to be very active in stunt kites. I'd definitely try the keel position first as the wing tips are a bad place to add mass, it will affect the inertia of your kite. And if your kite has a sliding weight on the keel spar, you could move it up to help adjust for the additional tail weight. Of course, it won't be enough but it would help. And as it burns the weight will change. Plus you won't have control of when it goes out.
Watch out for grass fires and check with event organizers!
Dave