I think that that fear of getting a thick trunk is overrated. It's not as if one day you will suddenly wake up thick. I can tell you from personal experience that weighted High and Low Woodchop(ers) are very, very effective exercises that will quickly develop both upper and lower portions of the obliques, and provide rapid development of the so called Apollo's belt, the v shaped muscles pointing down into the pelvis. They do develop quickly with these exercises but if you watch your body at all, you will know long before you get thick.
Unfortunately, no weight can spot reduce fat. As guys we store fat on our lower abdominals first and take it off there last. The only effective way to get rid of it is with cardio activity. In repeated studies the best cardio for targeting overall body fat reduction and abdominal fat reduction is the High Intensity Interval Training. You can google that or check my post on the forum regarding the best form of cardio.