I am surprised that the so called expert could not figure out that that tiger is a little much for that baby! Anyway some things you can do short of downsizing the engine would include any all of the following:

use a OS F glow plug(especially in an inverted engine)
decrease prop pitch
use a fiber prop(heavier for desired flywheel effect)
use a spinner for added flywheel effect
use a fuel with more nitro and oil
insure tank center line is 1/4" below carb center line.
make sure fuel line is as short as possible from tank to carb.
and probabaly a hundred of other things but without being able to try some of the above and evaluting your needs it is difficult to be sure.

Good luck