To expand on Solkan's answer;
BRB page 66:
If the players need to measure a range involving the embarked unit (except its shooting), this range is measured to or from the vehicle's hull
Psychic Hood on Page 56 of C:SM
Declare the you'll use the psychic hood after an enemy model within 24" of the librarian passes a psychic test.
By combining the two rules, and NOT inventing any rules to fill gaps:
1.) Psyker in Transport passes psychic power test.
2.) Declare you'll use the psychic hood.
3.) Check range to hull of vehicle.
4.) Proceed with Leadership roll off.
We didn't invent any rules there. We did exactly what the rules said. So by this, I can't see any reason why a psychic hood wouldn't work.