How to rip unparallel on table saw?
There are a few ways to do this. If you don't mind holes in one face of your board, you can screw another board to it at a bias, matching the angle you wish to cut, and lapping past the side of the board you're cutting. By sliding the temporary board along the fence, your workpiece will be cut at an angle. 

Another approach would be to fasten (with masking tape or whatever) spacers of tapered thickness to your workpiece, say every foot. Slide those against the fence. 

Finally, purchase or build a taper jig that does basically the same thing as the other suggestions, but is more versatile and reusable.