If i was training for a fight right now, i wouldn't run. I wouldn't want to train to match the base pace. I'd train so that I'd be setting the base pace and I'd set it faster than my opponent was comfortable. My roadwork would be at least fifty percent sprinting, running bleachers, etc. If I'm fighting three minute rounds, its going to be no comfort to me to know that I can keep up an eight minute mile for five miles. I want to be able to perform at balls to the wall strength and speed for the whole fight, and thats how i'd train.
But thats a different thread, the subject at hand is that the kid wants to put weight on but can't because he runs too much. He wants to stay fit and lean. Distance running is extremely catabolic and he needs to cut it out, period, instantly if he wants to start packing on the mass. The size needs to be his first goal, anything detrimental to his first goal needs to go away. That doesn't need to mean keeping fit and lean can't be a strong secondary goal. Sprinting is a fantastic replacement for jogging, knocking rest periods down to maybe 45-60 seconds between sets (less if you're fit enough to lift at high intensity, if not, a minute seems a decent goal to work to over the next month) should let him perform at plenty of intensity for his weight lifting while keeping his heart rate up. Because the real goal for the next six months should be to hit the weights hard and as frequently as possible.