Use 'C' key for crouch, thats my current setup nd its fairly easy to do the slide motion.

the way i do it is hold shift down with my pinky and use the rest of my pinky to press down the ctrl key.

the left side of the keyboard is actually slightly pushed away from me making it angled << allows me to relax my picky over both the shift and ctrl key at the same time, it actually for me makes it very comfitable to use.

i don't use C for crouch which allows me to rebind it to something far more useful like Interact or Nano Vision, allows me to keep the Q and E for nano stuff - F for melee and mouse 4/5 for grenades and using support bonuses, i also rebound middle mouse to switch between weapon attachments