There are several ways to provoke suicides, the most well known one from the trailers being to wait until a guard shoots at you, freezing time, possessing him and moving in front of the bullet. I found this very difficult.
A much easier one is to fry people in a Wall of Light. Unfortunately, this does not seem to work with rewired walls, as _you_ have rewired the wall and hence _you_ have killed anyone who walks into it.
The best location is therefore the Wall of Light in the entry hall during 'Lady Boyle's Last Party'*. Possess guests and run them up close to the wall then jump out - they will stagger forward a step or two to vomit and get fried by the wall. You have an ample supply. Just don't be seen by a guard possessing one of them (as it triggers their alert response and the Overseer with the giant music box will make life difficult - you could first possess and deal with him if you like). Save after every kill and you should be fine. In addition, you cannot rewire this wall, so you must suicide guests into it, as guards and the three Boyle women will not trigger it.