Setsul#2733
Budget?
Full set of cables is going to be rather expensive, so you can try customer support but I wouldn't bet on it.
Once you removed everything (maybe take the mobo out of the case) it should be easier to get a good grip on the cable (especially the lock) and remove it.
I've removed the mobo before just to make sure things would be removed easily for when I do decide to upgrade and that cable was just NOT having it.
As it stands since I bought my CPU already. maybe $200... $300 if necessary. Its possible to purchase singular cables for modular PSUs from Corsair (with shipping right now is $4.89).