An actual clog is rare with ConeColor or Piezography inks... but if you believe the ink lines are full and no air entered the system - you could purchase a single LLK cart fill it with PiezoFlush and run the INIT FILL procedure - it will purge ink from all the lines. But it is the most effective way to remove a clog.
Are you certain that no air got into the LLK line? Can you see any bubbles in the LLK ink line? Do you know if the cart got really low before refilling? Are you basing the 3/4 full off the Status Monitor or by actually removing the cart to take a look?
If air got in the system it is dangerous to continue printing. You can run the INIT FILL using the Epson Service Utility software available from 2manuals.com and that will charge all the ink lines with fresh ink.