Can you not make adaptor cables with inline fuses like a mini extension? You could make singles so each cable was fused or a triple which would take three cables pass through a single fuse and back out to three cables?
To prevent confusing the newbs/non-technical folks, please keep the terminology straight:
Wire = a single conductor
Cable or cord = a group of 2 or more wires that are ran together
The PCIe plugs use 3 wires in parallel for power and 3 in parallel for return aka triplets
Ja one could fuse each +12v power wire using 10A fuses or as you alluded to, use a single 30A fuse for each triplet.
Just cut the power wires (usually yellow) in the middle and tie together so you get:
power triplet from PSU > 30A fuse > power triplet to PCIe plug
Easy peasy and highly recommended when using multi kW PSU's to run multiple miners off of the 1 monster.