The Gangrel are difficult to manipulate, not because of any traditions or problems we have with them, its just that they themselves are so overtly unmanipulative that any attempts to pussyfoot around the subject feels out of place in a conversation with them.
The way to manipulate a Gangrel is to lay everything on the line, or to present the impression that you have. The problem lies in attempting to give them the impression that you have told them everything you know about a situation when in fact you have left out several vital facts. If you lie to a Gangrel, lie with confidence and remember, always remember that back door. Nasty things, with big friends sometimes.