This is another one I picked up off the web somewhere, most likely a forum (I used to have a habit of doing a copy/paste when I read something cool and/or useful). This isn't so much as scratching, rather it is simulating the sound of scratching. It will never replace the real thing, but might be enough to get you back on the creative path if you've hit the wall.

First up make an audio track and set it to 'resample', then mute everything other than your drums. Use session view to sample a one bar clip of your beat.

Load the sample into the simpler. Make a loop, setting the length to 1%, and set the fade all the way up. Set the sample start to 50%.

Now you'll need to draw an automation ramp for the sample start. Set the range from -50% to 50%. Now play your drum loop with the simpler. If you've done everything correct up until this point then it should all be sounding relatively pretty normal.

Now you need to create some patterns by playing around with the sample start and transpose to create vinyl style stops, scratches and those old school granular time stretches.

Now you just need to sample these patterns, move them around to arrange them, and cut them up to make fills. Done.