Working on Sustained Power for the Bike

I had an interesting conversation yesterday about training with a former time trial national champ. What made it interesting is he knew about everything I needed to do to train for the Transylvania Epic. There's not a lot of people you can strike up a conversation with about max heart rates, lactate threshold, and sustained power. The power part was the part that made me think a little more -- power on the bike. Right now, I'm in a "sustained power" two-week training period. Years past, "power", to me, meant hitting the leg press machine at the YMCA and gradually building more powerful quads through heavier and heavier weightlifting. I'd do squats, lunges, and step-ups to build what I thought were stronger legs. The plan I'm currently doing, though, states "we aren't trying to be body builders," and there are NO weight workouts. At first I thought, geez -- how will I build strength? After a couple sessions of big gear riding at a higher heart rate, I'm finding the power coming without the weight room. The average mph at the same HR is starting to creep up. It doesn't seem quite as hard to push the biggest gear I got like it used to and the knees aren't aching afterwards. I like that. But boy am I missing the mirror monkeys at the gym.