For conditioning, I've always found reverse sit-ups to be the best exercise for the lower abs. By reverse sit ups, I mean the kind where you lay on your back on the floor, and lift your legs and then butt into the air. Try doing them in a straddle, too. You can also do this hanging from a pull-up bar or holding onto your pole. Another possibility is to do triple sit-ups, where you lay on your back on the floor, then do repetitions of three different sit-ups: a tuck, where you lift your upper body off the floor, arms extended at your sides, and tuck your legs up at the same time; a straddle, where you do the same thing, but legs in a straddle (try reaching your arms between your legs on this one), and a pike, where you lift up with your legs straight.