Fair enough!
I don't know if you could almost consider it a separate "experiment" - keep the expressing and EBM bottles and just attach when he would not normally be having a feed to see what happens.
He's much bigger and stronger, he has something in reserve, you know you have a whopping supply and you that your supply responds to pumping - so it would be pretty safe to give it a try. It's just such a monster workload for you...
hugs.