Lay the PC on its side or if possible lift it and tilt it so the radiator is facing the floor, that will allow it to fill. You will get a lot of air bubbles to start though, just be sure your res is as full as possible each time you fire it up.
edit: and jesus effing christ, clean that thermal paste up boy!
you wont be managing to get that much over it with the AS5, that stuff spreads like cold marmite