I dont know i also have this problem, but after reading up about this model people are saying it is tail heavy even with the battery up front, so i would advise not to use the ducted fan and just bolt the motor on the back instead to have a chance of getting the C of G in a reasonable place.
Thats what i am going to do anyways.
I have also got another motor for it thats lighter and has more power as i have heard the motor provided is a bit on the lame side with the plane having no power in the vertical.
All in all i think it seems to be a poor kit but a am going to try and make the most of it, keep it nice and light, use a three cell lipo to help keep the weight down.
I hope we have more luck than some of the people i have heard about with these.
Have also been told the C of G location as given in the distructions is wrong and should be aprox 157 instead of the instructed 170 odd or whatever it states.
Have not finished mine yet so carnt tell you how i get on with my setup.
Would like to know how you get on though ! all good tips apreciated.