When sharpening router bits with a diamond cards, I doubt that you really need a lubricant.  The main purpose is to sort of float away the swarf so that it doesn't clog and you just won't generate that much.  If you do, just brush it off with an old tooth brush and keep going.  

--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.