Great question. It's a bit tedious. For the specific C0 code you wanna step thru, make sure it's your very first code in your Cheat-Manager. Then in Dolphin, set the Boot to Pause flag (can't remember where this is at). Make sure your codes are applied, boot your game. The emulation will auto pause on the very first executable instruction of the game.
Then go to 0x800018A8 in Code View. This is the start of the Code Handler. Once at 0x800018A8, start to scroll down and search for the following two instructions..
mtlr r15
blrl
These are the instructions that the Handler uses to execute all C0 Codes. Once you find these two instructions, set an Instruction BP on blrl. Unpause the emulation. Once that BP gets hit, your emulation will pause itself then you need to simply use 'Step-In' just one time. You are now at the first instruction of your C0 Code. Set a new BP on said instruction and remove the previous BP. Thus you only get a BP hit on that specific C0 code again if you decide to let the emulation run again.
Then go to 0x800018A8 in Code View. This is the start of the Code Handler. Once at 0x800018A8, start to scroll down and search for the following two instructions..
mtlr r15
blrl
These are the instructions that the Handler uses to execute all C0 Codes. Once you find these two instructions, set an Instruction BP on blrl. Unpause the emulation. Once that BP gets hit, your emulation will pause itself then you need to simply use 'Step-In' just one time. You are now at the first instruction of your C0 Code. Set a new BP on said instruction and remove the previous BP. Thus you only get a BP hit on that specific C0 code again if you decide to let the emulation run again.