You're totally dead meat. totally doing Warhammer 40K wrong.
Oh wait, this is a forum where we help people. Not DakkaDakka. My bad!
Okay so two things come to mind:
1. If the wording is specific you're golden because Raiders can be taken as Fast Attacks, not JUST Dedicated Transports. Hooray for you. So this restriction is actually NOT an issue. The Raider is now like a Land Raider. It can be taken as Dedicated OR as a slot.
2. 3 Liquifier guns on the Grotesques?
Hold out bait to entice the enemy. Feign disorder, and then crush him.
-Sun Tzu, the Art of War