We used to just play it like baseball, in the street, with chalk marks on the curb, or else a brick or something next to the curb which would mark the "base".
Yes, I suppose American Baseball may not be familiar to those across the pond, although there is an English World League Baseball team (the London Teacups).
Eventually we grew bored with the non-painful game and came up with our own rules, based something on raquetball and suicide:
The game is played with a large wall and a hard but bouncy rubber ball. Since the Wiffleball bat wasn't really strong enough for this type of ball we'd usually wrap the bat up with black electrical tape first. This made it much stronger and more painful.
The "fielders" would stand behind the batter in varying distances. There were no teams - everyone would have their own personal score. The batter would serve the ball to himself by throwing the ball against the wall, and then would hit the ball (again against the wall) and run around the bases WHILE CARRYING HIS BAT. If someone caught the ball off the wall with no bounce first they'd then get to try to get the batter out by throwing the hard ball at him. If they missed, someone else could pick it up and try to tag the runner/batter with the ball. The batter could try to fight them off from doing this with his bat.
If the ball touched the ground first someone could still pick it up, but if they threw it at the batter and missed the batter automatically received a point and got to throw a penalty throw at the fielder, who would "assume the position" against the wall (facing the wall, legs spread apart, hands on the wall, and head down, if he knew what was good for him). The batter would then stand back on the batter's box and would throw the ball as hard as he could at the fielder. Body shots earned you an extra point, arms and legs were no points, and if you missed, you changed places with the fielder who would then be able to get a penalty shot off of you.
Batters kept batting until someone threw or tagged them out. The rotation was just an arbitrary order, and everyone kept track of everyone else's score.