Here is another way that totally excludes the thrust vector and is very easy / safe to do:

1) Climb pretty high
2) Go to idle, leave the flaps up but lower the LG as it may affect the CG and you probably want to optimize for when the LG is lowered.
3) Turn into the wind, right in front of you.
4) Start a 45 degrees dive, release the stick

If the plane accentuates the dive angle, it is tail heavy. If the plane recovers very quickly by itself and balloons up, it is nose heavy. If it continues down at 45 degrees or slowly recovers, it is right on.

I have yet to do this on a jet but this is how I usually do it for gliders and pattern planes.

Arnaud