Yeah you can scuff them with some sand paper like 80 to 120 grit.
Just take the pads all the way out just like you're doing new pads...and if you can lay the sand paper flat on a bench or smooth ground and slide the pad back and forth until the whole pad has changed colors. Then, clean them up with some brake cleaner, get all the dust out.
You can do the same thing on your rotor, just leave it in place or take it off and hold the sand paper in one place and spin the rotor...knock off any rust chips.
A lot of times, you could have some type of build up of material in that pad...like a chunk of ceramic or even metallic as I believe most ceramic pads still do have some metallic in them...just from the manufacturing process. If this is the case you'll probably notice a ring around the rotor in that area.
Personally, if I was taking everything apart, I'd probably just buy a new set of pads if they were down around 50% anyway...but that's just me.
Also, don't forget to lube where the pad seats with a synthetic brake lube, and clean it up first of any rust or build up because that will help cut down on heat -- which is what makes your rotors and pads glaze up in the first place.