I don't really see the need for it.
Last night I bullrushed a chaladin for 2d10 (16) off a cliff into some water. If not for feystep, he would have had a hard time with those swimming and climbing checks.
Before that, I bull rushed another player during a gameday down a 6d10 hole. Even gave him 3 saves, one for the initial fall, another to grab the arm of a guy who'd i'd dominated down into the whole prior to him, but had caught a ledge 40 ft down, and a 3rd save to catch his own ledge. Thankfully, the damage was low, but the rest of team was hurting with 2 ppl out of combat.
I've bull rushed players off of boats into the waiting jaws of weresharks, or just off the boat and out of combat. Pushed off bridges into strongly flowing rivers, forcing swim and endurance checks, also forcing the party to venture downstream to find him.
Had a horde of minions (10) bullrush chage a paladin 5 sqaures onto a teleport circle that the big bad activated to zap him out of combat.
Bull rushed a rogue into the path of an oncoming boulder... A warlock off an airship... a cleric into a gelatinous cube pit trap... warlord into a sewage pit... barbarian into a brazier and set him on fire... the list goes on.
If all you have to work with is flat terrain, you need to tell your DM you want some elevation changes to play with, otherwise, look for need things to do to get players or monsters out of combat. Also realize, if the players start adding fancy stuff to thier bull rushes, so will the DM
