From what I have been reading because I have just gotten a T-Rex 500...
the Van-de-Graaff generator effect is because the 500 has a plastic tail and
the boom goes into a plastic housing on the main frame.

The 450 has metal tail... metal tail block on the main frame... so supposedly
Van-de-Graaff generator effect is eliminated. But you said you taped off both
ends of the tail boom.. thusly insulating... and isolating the tail boom so maybe
the Van-de-Graaff generator effect is now possible.

Some people that have been talking about Van-de-Graaff generator effect in the T-Rex 500's
are coat their nylon main gears with Static Guard... the generic stuff and say that
eliminates static build there too... it's cheap stuff and it wouldn't hurt. They spray it into a cup
and use a brush to apply.
On the 500's they are also grounding the boom to the main frame... there is a lot of discussion
about this http://www.helifreak.com/showthread.php?t=61205

You might consider replacing the tail boom with a proper fitting one that you don't have to tape off
the ends. Your old belt may have been frayed enough to cause extra friction and thusly the
Van-de-Graaff generator effect.

Spraying your belt there are lots of discussions on this too... I use "pure" silicone spray.

(and if I have misspoken here... please be easy on me as I am a noobie... one year flying.)

Walkera 22E - Copter X 450 - T-Rex 500 (all electric).