I was looking it over in the garage. I don't think sliding is possible, economically. But there are only 4 bolts holding the tourpack in place and an additional 2 holding the small pad in front of the tourpack.
I think a plate (steel or aluminum)of some kind could be built to attach between the current brackets and the tourpack to move it forward 12 inches. I'm going to unbolt mine from the brackets to clean it this week and I'll see what it looks like sitting forward like that.