Elites - Lictor Brood
Stats, brood size and all existing special rules as in Codex: 'Nids, except remove Deep Strike.
Force them to stay in reserve regardless of mission.
Bump their cost to 90-110 points.
Only allow them to deploy in cover or out of enemy's LOS, and count them as Infiltrators for the purposes of surveyors and auspexes.
Give them either Beasts or Fleet.
Give them a Tyranid equivalent of Polymorphine.
I think that'd really have them fit the fluff a little better - instead of getting shot before being able to strike, they'd pop out of nowhere, stuff some screaming victims down their throat and bugger off to do it again the next turn. An auspex would give their intended victims a chance to ward off the attack, but unsuspecting congo lines of infantry would have their numbers whittled away.