The VeraCrypt guide recommends "You should use the decoy operating system as frequently as you use your computer. Ideally, you should use it for all activities that do not involve sensitive data." You don't need to fake it per se, but section off what needs to be in the hidden operating system (rather than a standard VeraCrypt partition). You are therefore revealing real, thus plausible, information, but not the actual subset you want to hide.