You can stick them on with double sided tape.
As a special I scrambled my cube beforehand with the following algorithm:
F2 L2 B2 L2 D' U' B2 D2 F2 R2 B' F' R2 D U'
And then I chose one shape for each side and printed the faces in the color the flat faces were before. So I created a Cube with two solutions: Splve per color and solve per Shape.