Well I FINALLY found an attack... or rather sequence of attacks that works very well.
With the exception of raw Force lightning, Paratus seems to be immune to everything else. There is one tactic I found to work almost every time: Aerial Assault followed by a push push. When locked on to him(R1), jump into the air (A) and dash at him (L1). He will block this attack, but quickly follow that with Force Push (B). This will often knock him on his back and give you some time to recover Force energy before you go at him again.