Or... clean a long screwdriver. Rest the tip of the screwdriver in the port on top of the SU. Place the mouth of the oil bottle against the screwdriver shank and begin to pour slowly. The oil will flow down the shank of the screwdriver and into the carb. This is also handy when pouring DOT-5 brake fluid into the reservoir as a method to minimize bubbles in the brake fluid.
Another alternative if you like either 30W or 20W carb oil is to use 3-In-1 oil in the small bottles with the squirt tops. The blue 3-In-1 is 20W, the red is 30W.