Seriously, if it is an emergency - which a jammed throttle arguably would be - you will have called Mayday and the Tower should render all possible assistance
That assistance can (and should, in case of a low-hours pilot) also include phoning your operating base, getting your instructor (or for that matter, any instructor) on the frequency, to calm you down, to reassure you and to give you advice such as this.
Heck, if experienced pilots are monitoring the frequency (and in case of an emergency, you can expect they will) and they figure out you're close to panicking and the tower doesn't do anything about it, they will jump in with some sensible advice. (Remember that the tower controller, although the authority on the frequency, might not be a pilot himself, and might not know tricks like the ones mentioned.)
As others said, in an emergency all rules go out the window. (I was assisting in an emergency a while ago and accidently flew too high, into class A airspace. Didn't hear any word from the tower about that, although they were radar vectoring me to the scene so they must've noticed. Only until the - fortunately undamaged - aircraft and occupants were in sight did I get the polite question whether I would be able to descend a little.)