Mostly disarm is most easily handled as fluff. The problem with tactics that 'defeat' enemies without reducing their HP is they are either invariably better than normal fighting or worse. Some ways that disarm can be fluffed in are:
1) Enemy reduced to 0 hit points
2) Enemy forced to surrender with an Intimidate check (which can be made to work off STR with a feat).
3) Plot specific mechanisms that the DM may introduce for story reasons, in which case it could be a skill challenge or use page 42 (stunts).
Those are the most reliable, though if the page 42 method is TOO easy, then PCs may want to do it all over the place. Given that 4e also has things like minions that are defeated in a single hit you can definitely get in a decent amount of "disarming" without needing to make it a standardized tactic.
It is notable that doing it consistently via hit points also means it is unlikely you end up with PCs getting disarmed randomly as well. Especially in 4e losing your weapon at higher levels is bad news.