It's hard to tell you something without knowing the whole context but
in principle the answer is no. You can't give a "trial lesson" without a) a registered training facility b) a supervising FI and C) an aircraft insured for Ab Initio training. Many syndicate aircraft don't have this because it's much more expensive.
The flight experience is part of the PPL syllabus so it's a lesson like any other.
So that's the literal interpretation of what you asked.
If you want to take a non paying passenger up for a flight and let them have a go, you can do that, you can probably even practice your patter but it's not a loggable flight and they should not be paying you for it.