One option is the C-clamp that fits desks with thicknesses between 0.39 to 3.15 inches. The other option is a grommet mount ...

which drops a quad of USB ports into one of the 2-inch grommet holes found in many desks. If your desk lacks such a hole but you still want a flush-mount hub, the folks over at Make have a DIY ...

Easy to position the laptop to your perfect angle only with one hand. Detachable Tray Design: Mount plates have mounting holes 75x75mm and 100x100mm. You can replace the laptop tray with displays.