If they use HBK they should have him get destroyed by Lesner.
That way HHH can get more on his side for revenge and it'll make Lesner look like more of a monster heading into the match cause on Raw 1000 it was HHH standing tall after he cleared Lesner from the ring. Not to mention HBK is an awesome seller and would make Lesner's attack look even more brutal. WWE would love showing 10 replays per Raw of that attack... lol
Great idea but I doubt Brock will be on Raw tonight, he'll maybe do 1 more before Summer Slam but I think if they do anything it'll be a Heyman promo.
With that in mind what they should do is have Shawn come out, get his big home town pop, let him do his thing. Bring Hunter out and have Shawn sell the fuck out of the match, not so much "put over" Lesnar but kinda be like "Hunter, this Lesnar is a fucking animal, he's younger than you, he's in better fighting condition, his rep speaks for it's self...are you sure you can handle him a Summer Slam?" Have Hunter put over how bad Lesnar is but also, at SS it's going down, he's gonna end "the big bad" Brock Lesnar.
Have Lesnar's music hit, out comes Heyman...don't have him get in the ring, but on the ramp have him cut a promo saying he got Heyman to agree to the match but it's all good, that was just Stephanie signing her husband's death warrant, Lesnar will tear him apart, blah dee blah, "at Summer Slam it will be Game...OVER!". In the following weeks I'd start airing Lesnar "training videos" of him lifting weight and destroying guys.
Iceman's idea is better but that's my take on it if you don't have Lesnar there in person.