On Stalingrad if you know the grenade jump you can do this one, it requires 2 people to do though.
When you're on the roof above the train one of you has to crouch and have their back to the other person.
The other person who is not crouched has to run and jump on the persons back or head, and then they can jump on the middle section of the roof.
This is better than grenading yourself because it doesn't give your position away.