1. It is (physically) possible for some people to jump off a cliff.
2. It is (physically) impossible for NonSuicidalGuy to jump off a cliff.
Or
It is physically possible only for some people to jump off a cliff.
Or
1. It is physically possible for NonSuicidalGuy to jump off a cliff, if he wanted.
2. It is physically impossible for NonSuicidalGuy to want to jump off a cliff.
Another way of putting those statements would be:
1. It is (physically) possible for some people to jump off a cliff.
2. It is (physically) impossible for NonSuicidalGuy to jump off a cliff.
Or
It is physically possible only for some people to jump off a cliff.
Or
1. It is physically possible for NonSuicidalGuy to jump off a cliff, if he wanted.
2. It is physically impossible for NonSuicidalGuy to want to jump off a cliff.