1. Switch to heavy bag work and run a lot less. Heavy bag work builds fight type endurance. Long running burns calories you need to grow. If no bag, go burpees.
2. Eat a ton. I recommend: potatoes, lots of fish, lots of chicken, lots of beef. Cottage cheese, milk, protein shakes, tons of fruit and veggies (for critical vitamins and minerals), multivitamins and weight gainer (for extra calories).
3. Lift like a hoss. No pansy machines. Deadlifts, Bench, Squat, maybe some cleans and jerks, and assistance lifts for those. Remember, try to go up in weight. It's fuckin' work. Try to keep workouts between 45 minutes and an hour. That causes the release of the most growth hormone (read it somewhere, not sure where exactly). That doesn't mean slack off in your lifting, that means lift like you fucking mean it. Start doing a lot of stretching; it will pay off wihen you start BJJ.
4. Sleep a ton. Take a nap if given the chance. Get at least 8 hours a night. Sleep with no lights, no music.
You will pack on some muscle.