Stacks of over 64 in storage blocks?

I've seen some shulkers on 5b5t and they have put stacks of over 64 items in one slot. This is perfectly possible in your inventory when you craft dupe. Like you get anywhere from 63-75 items when you dupe. But I'm focusing on 65-75.

Id like to know how to get over 65 items in one slot in a shulker/chest. I've tried abusing auto32k on most hack clients and other inv-related hacks. Not sure how it would be possible or if it is just not possible.

-PapiFlasKY