Is it possible to perform zero offset calibration without unclipping?
Like coasting or pedaling backwards.
Does this "fix" zero offset issue until the next sprint?

This crankset?
https://aliexpress.com/item/1005009333438182.html
I don't think you will find easton specific spacer.
Try to find a generic spacer that fits (external/internal diameter, width).
This is something FSA uses for their boost/non-boost MTB cranksets.
https://www.bike24.com/p2307774.html?sku=1076120