You can extend the fuselage a little farther out so that there is more torque provided by the battery and motor.
Take off any unnecessary weight from the back of the plane.
Can we see a picture?
How much glue and what type of glue did you use?
I have not found the FUNBAT any tail heavy. What have you done? Not followed the instructions?
On my "indoor" there is a 24 gram motor in front and a 25 gram battery - "anywhere" - total weight 160 grams.
On my "fast" outdoor i have a 55 gram motor in front and have to push the 75 gram battery as far into the body as possible.
I use 6 mm depron as stated on the BloodyMicks page.
Paper, covering,thick paint or to much glue will make the plane heavy - that is of course the same for all models.
Any reinforcements are not needed for the light version. I tape the sides of the front until about 3 cm under the wing for the fast and heavy version.