If you put an appropriately-sized rod inside the steerer then clamp on your old-stem-cutting guide, would the compression be enough to limit delamination while filing?
You could try that, but the pro tip is to freeze the part into a block of ice and then do all your cutting using liquid nitrogen as your coolant. And yes, those are actual strategies for machining composites.
If you put an appropriately-sized rod inside the steerer then clamp on your old-stem-cutting guide, would the compression be enough to limit delamination while filing?