I cleaned the mat with Goo Gone. A couple of squirts are enough. Use a little piece of paper towel to spread it all over and 15 minutes after, all comes off with the scraper. Put some more a second time if you still have some goo.
Wash the mat thoroughly with dish soap to remove all the grease from the goo gone and dry it well
Put some masking tape on the borders. This is very important. You don't want your machine's rollers to get stuck to the mat.
Apply ONE even coat of Repositionable Adhesive. I used Scotch® Spray Mount™ and found it to be too sticky that some cardboards got torn when removing them.
I had to put my mat upside down on my carpet to make it less sticky and that worked great. I've seen some people using Aleene's® Repositionable Tacky Spray Adhesive, Krylon® Easy Tack Repositionable Adhesive Spray, Elmer's Repositionable Mounting Spray Adhesive and Martha Stewart's® Stencil Adhesive Spray.
Have you tried any of these? please share your thoughts.