Well first thing to do is to creat a totally transparent icon (With Apple IconWorkShot demo for example).
Be aware that you will not be able to delete the icon in your Circle Dock if you put the blank icon on it (not possible to select it). So here is the best way to make your presentation.
1) choose the number of collumn and circle you want (Icon/cercle) and create basic icon to fill even not desire spot
2) one by one arrange the disposition of your programs (you can try dragging but it doesn't work so well)
3) Change for transparent icon the spot you want to desapear
Once pay attention that if you make a mistake, you'll have to do things from begin -> Save your configuration when it's done.