Please PM meThis shows what kind tool is used for crimping Mini-fit connectors.
If you can't see the inside of your PC, you could always cut the cables in the middle, shorten them and use in-line crimps to rejoin them together.
It's not ideal as the crimps add volume and you would need to stagger the positions of the crimps otherwise they would form a massive bunch in the middle of the cable.
If you don't have the crimping tools, but you can solder, you could always shorten and resolder the cables within the PSU.