I need a stimulant to get me through work on methadone tapering, what should I do?

Don't. Don't depend on other drugs to get you through the tapering of one drug.
Slow. Slow down the taper is the first choice. Next would be a cup of coffee. Except for cancer patients i avoid adding stimulants to methadone. The good news is the fatigue will get better with time. At most i would consider a week or two of modafinil.