It's totally do-able. If you are allowing the valance to dip between the knobs you will need to attach a contrast skirt to hang behind the valance. If not, the top of the valance can be stapled to the board. I usually serge the seam across the top instead of sewing and turning it so it will allow you something to pull up over the board to staple to. Give me a call at the office and I can go into further detail.
Note: You will need to stretch the valance out so don't cut the board until after you have done so and get an accurate measurement.