Where exactly is the oil leveling plug hole? If there really is one, it seems to me a good procedure would be to:
warm the engine & transmission
remove transmission drain plug - (about half of the 9 quarts will drain)
remove transmission oil leveling plug
remove transmission oil filler cap
fill transmission with new transmission oil until oil begins to drain out of the oil leveling hole, establishing the correct oil level (no dipstick needed)
replace oil leveling hole plug and filler cap