You should not have to overfill it!! Just remove the fill plug and it will drain to the proper level!!! I had a hell of a time filing my T-5 from underneath cus I did not have a hand pump. I ended up having jiffy lube drain and refill my rebuilt T-5 after 500 miles cus I wanted no part of that chore again
Never thought of pouring in through the shifter, but why not just get a small hand pump and fill it the right way. Taking off the inner boot was not much of a fun thing either, and mine got all ripped up in the process, only 4 trips to the dealer and $32 later finally got me my new inner boot!