1) Buy 1/8 inch thick basswood from an art supply or hobby store
2) a) Download bitbeam-arduino-plate.dxf and lasercut it!
b) Download bitbeam-arduino-plate.scad, modify it in OpenSCAD, export to DXF... then lasercut it!
3) Use three 1/2 inch long, 4-40 steel machine hex screws and nuts to attach your Arduino to the plate.
4) Write a comment here saying you've completed steps 1, 2, and 3!