Mmmm, no.
The basic idea is flawed.

Why?
Because there's almost no THC in the roots or in the sap.
THC and many other cannabinoids are synthesized in the resin glands.
Those glands use the power of light to assemble our favorite chemicals from their precursors.
Dipping the roots in hot water just might force more liquid into the stalk, or it might cook all the pores and shut down transpiration.
A brix reading would shed some light there.
But it will not force more resin into, or onto, the buds.

That said, "There are more things Horatio, in heaven and earth, than are dreamt of in our philosophies"

So, if you want to try it anyway, I suggest an experiment.
Sample two plants at a time.
Dip one, do not dip the other.
Compare them for potency.
(That's the fun part, I'll be happy to help)
Then come tell us what you find out.

Aloha,
Weezard