You could always just describe to them the changes you are interested in (based off the morph someone did on here).
But if you're really wanting to show them the photo, i'd say something along the lines like Slysurfz mentioned.
Just approach things in a non-challenging, laid-back, easy manner.
Like you were messing around in photoshop, and was wondering if this was possible.
I don't think there going to be upset or mad if you use an honest, non-challenging, and straight to the point approach.
Don't act demanding when showing them a photo, ask him if this morph you made is even possible.