The Wiki on Fast 7 - Filming mentions (and shows an image of) one particular example at the end of the film.
Paul's face is CGI'd over whoever's torso they used for that scene. It is vague on the matter of other scenes though, simply mentioning that they also used it in scenes newly written to support the concept of Brian 'retiring' from Dom's group1.
That particular image would have been as Brian pulled up beside Dom, chiding him for leaving the beach without saying goodbye.
- I expect those scenes were when Dom/Mia/Brian are in conversation as to him 'missing the bullets' and possibly the mini-van scene at the school (showing his awkwardness with family life).