The way I see it, you have at least two options depending on when you submitted the original amendment.
If you submitted that amendment a while back, wait and then apply for the TIB (along with any other changes you may need to make that are priority).
If you don't want to wait and then apply for the TIB, do this: call the NRC, provide the amendment ID from PONL, the NRC rep will give you the name and contact info for whoever the amendment has been assigned to, e-mail that specialist with the ID number in the body of the e-mail and ask that it be withdrawn. The specialist then should (in pretty short order because it helps their clearance rate) withdraw your application for amendment on your behalf.
That's worked for me in the past.
Good luck and, if you don't mind, please update this thread with how long the amendment took to get processed.