You cheat using CWCheat as you already found out.
How didn't it work for you? Did the program work at all? Did when you open CWCheat your game not show? Was it the code that didn't work? Did you look for any other guides for CWCheat that may be a bit more extensive than that guide?
The only other way you may want to do it is to ask someone nicely to upload a save file at the start of the game with cheats already implemented that do not need to be active (some gameshark codes must be active in order to sustain their effect, others may need to only be turned on once - like Max hp, vs current hp... max hp only need to be initiated once, current hp would change with the value of the code and when it is turned on.)
You really should be able to put CWCheat on your psp yourself. It is a simple plugin.
Also you should make sure that CWCheat has been enabled in Recovery mode, which that guide you linked to does not even mention.