The key here is using Feral Vision until you know the common environmental items to use to complete this; these include pipes, fork lifts and anything else protruding or explosive (explosives to be confirmed). Once you find what you can use in your environment you want to normally do one of three things:
a) stand near a sharp environment object, when an enemy approaches, hit *grab* to initiate an automated animated kill
b) *grab* an enemy and use the left stick to throw it towards a shard wall object
c) hit explosive objects to explode them near the enemy units (this to be confirmed)