Your hypothetical is missing the part where the rocket pods tear the B-52 apart and a flaming ball of debris falls to earth. You see, to accelerate straight up

Your hypothetical is missing the part where the rocket pods tear the B-52 apart and a flaming ball of debris falls to earth. You see, to accelerate straight up (or nearly so) your thrust must be greater than your weight. To get enough acceleration to be useful, you usually need an amount of thrust that's more like 1.2x your mass. For example, the fully loaded Saturn V weighed about 6,500,000 lbs and the first stage had 7,650,000 lbs of thrust. So your fully loaded B-52 (~265,000 lbs) needs around 320,000 lbs of thrust from the rockets. This is more than double the amount of thrust produced by the jet engines. By the time you've accounted for your rocket engines, strengthened the airframe to survive the rocket thrust, and added a reaction control system (to turn around for deceleration), you've lost a good chunk of your 35 tons of rocket fuel. It's about this time you realize that even 35 tons of rocket fuel is a laughably small amount. A single space shuttle main engine is a bit more powerful than what you'd need (~420,000 lbs of thrust), but it's good enough for ballpark numbers. It will consume 35 tons of fuel in about a minute... meaning your mission profile is probably something like 30 seconds of vertical acceleration, 15 second horizontal acceleration, 15 seconds horizontal deceleration. Not enough to take you very high or very far. It's not that we can't do it, it's that it's woefully inefficient.