Using customized mob spawners, you were allowed to give mobs customized equipment with all of the normal information, including damage values. In this most recent version, durability seems to be bugged – regardless of what value I set for the damage, it seems to want to drop items with 25 durability remaining, with a rare variance. It never has the damage amount set in the NBT data of the spawner itself, however (well, maybe if I set it to leave 25 durability remaining).

For those who wish to test this themselves, you may use these two schematics (spawners, requires MCEdit) – you may also check the NBT tags in NBTedit for confirmation that there is definitely some sort of buggy behavior going on.