Pairing with a Vendetta is the only good way I see with guard. 2 command squads w/ meltas, a company commander for some shooting orders and maybe an officer of the fleet in there. Expensive, sure, but that's a serious AT firepower package, and pretty damn durable too.
Come to think of it, why not add a Vulture or two with twin punisher cannons, if you've already got an officer of the fleet for calling out ground targets? 40 S5 shots baby. If it goes to hover, stays stationary and shoots at designated ground targets, it hits on 2+... skydakka! Sure, that's a good chunk of your army right there, but a pretty cool chunk.