yeah, umm well Alaitoc does a nice job of that with disruption table. I'm thinking a model/squad that can use hidden setup and infiltrate no matter what, like the Callidus(I think). I once made an uber assassin which was very much like a harlequin but was great cause it could pop up anywhere and had an ungoldy amount of attacks that were power weapons and was insanly strong. little unfluffy considering they were eldar...but it had a nice thing. so create a character, or just say somethign like, one squad in your army gets to go after deployment but before turn one, gets to move shoot assualt basiclly get a free turn. that might work nicely.