Step 1: Don't bother attacking with Bankai, just summon Kyokotsu.
Step 2: Pull out Shinken Hakyoken, Go back to Shikai.
Step 3: Use Darumasan fell over and Shinken Hakyouken to cut Lille's head off.
Step 4: Then beat the crap out of the subsequent Flamingo Apocalypse.
P.S., this works because Shinken Hakyouken is always in Shikai, and it's effect is passive, so Shunsui can use it fine. Nanao didn't need to be there.
Step 2: Pull out Shinken Hakyoken, Go back to Shikai.
Step 3: Use Darumasan fell over and Shinken Hakyouken to cut Lille's head off.
Step 4: Then beat the crap out of the subsequent Flamingo Apocalypse.
P.S., this works because Shinken Hakyouken is always in Shikai, and it's effect is passive, so Shunsui can use it fine. Nanao didn't need to be there.