Fighting from a square which contains a corpse or object (no bigger than medium-size) is allowed and uses the following rule:
Any character taking a Standard action in an object-occupied square takes a -2 AC penalty while he remains in the square.
This rule represents the limited mobility in the square with an object or corpse (including tables, chairs etc.).
A Balance check can be attempted when the character wants to avoid the AC penalty. To do so, the character must use a move equivalent action to attempt a Balance check DC 15. If successful, the AC penalty is waived until the character's next action. Failure simply results in the penalty applying as normal.
This is helpful for characters who want to remain over a corpse or fallen comrade, essentially "protecting" them from coup de grace attacks, etc., or to simulate the cinematic "fight around the table" scenes where characters use furnishings to aid in their defense.
The balance check needs to be made each round for the AC penalty to be avoided, so a Balance check and standard action results in the character's actions being expended for the round.