I started commuting on a mountain bike, and added the trekking bars to get a more stretched out feel. This meant that I needed the levers out at the front. I was able to get a regular set of alivio trigger shifters/brake levers around the corners by using lots of grease and some effort. Some paint came off the bars (it was apparent in the grease), but the bars were not scratched - it didn't rub through the paint in any places. Just remember when you start to put them on backward, so they are oriented correctly when you get to the front. Also, you can cut the ends off of mtb grips and slide them to the front for a nice cushioned grip. I tried mounting them where I could reach them on the sides (neutral hand position), but I didn't like it much.
I think where you mount the levers depends on where you spend most of the time. I was trying to stretch out for some commuting speed, and so it was more important to have the levers where you can reach them at speed. I used the closer portions of the bars much like the top bars of a road bike, when going slow uphill or for whatever reason, and you have plenty of time to get to the brakes.
Sorry no pics anymore.