I bout the special wrench (adapts to a 3/4 drive) from somebody on eBay for 8.99 bucks) I believe it also works for other Honda bikes. The manual says you can make it yourself with a piece of tube, but for that price I don't want to waste my time filing a piece of tube that I don't have.
Once you remove the oil filter (pay attention to the position of the washer below the nut, the script have to face outwards on reassembly) you have to remove the oil pump. That way, you will be able to remove the clutch cage, that have a plunger connected to the oil pump.
Been there, done that.
Raul
P.S. Which manual do you have? May I assume none?