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Hi there,
Well, the only way i can think of is to cut the wire a few inches from the PSU and wire them into a terminal block, keep the remains in case you need to connect them again.
A more simple method would be to cable tie the remainder and hide them in the case like most people do, but i'm sure you already thought of that.
I would advise against opening the actual PSU to disconnect them, i have no experience of this and i doubt most people do, there are extremely high voltages within a PSU, even when it is turned off, plus it would void the warranty.
Be carefull.
Trill