1. Find any rail in the game.

2. Rail on it for 1 second or so (if you are using a controller wait until the controller starts to rumble)

3. Pause the game. Edit: Pause the game with using steam overlay (shift+tab) due to new update.

4. Come back after desired time.

5. Jump off the rail and wait until you get your points.

6. There you go. Your grinding statistics have now increased with your desired time.

(7.) If you didn't understand the Text Tutorial just follow the Video below.

Thanks to Bayonet Botan for finding the new exploit.

Edit: Rewrote the tutorial, added credits.