This is from Bovada themselves as I asked the same question:
You can buy points on NFL, NCAA football, NBA or NCAA basketball point spreads. When you do, you move the point spread by half a point so that you give away less points with the favorite or get more points with the underdog. You can only buy points using our full site. You can buy half a point onto a flat number only.
Below is the link on how you can buy points:
www.bovada.lv/.../buying-points