I know what you are talking about here. When I changed mine a few thou ago, I thought, how the heck do I get it back in without most of the oil hitting the ground instead of going in the case? All I did was take some tinfoil and made a wide "funnel" out of it by first shaping it to fit into the derby cover and under/close to the clutch, the I shaped the outer part enough so I could dump in the oil. No problem at all.
BTW, the stealer told me that 32 oz was just a fine amount when I asked about the level of oil, seeing a "quart" is 32oz and the spec is 38 for the case. Have heard this from several people.