First thought: drive by paintballing.
Paintballs don't kill, just don't aim for faces or children. A truck/van full of paintballers, in full gear so as not to be recognized, with the plates removed. From out of town, if possible. You can't sue if you can't identify.
Second thought: that's insane, collateral bruises, they'd find someone to sue anyway, dangerous, don't do it, etc.
I'd suggest a wall of people to physically stand in the way of the WBC. They can't get through without shoving, and if they do YOU can sue for all their campaign funds. If you can't get people for that, go for a counter protest. It's been said by others here: Funerals are no places for counter protests, but funerals are also no place for the WBC.