It is not illegal at all. Not sure if they are around any more but Omega used to make some tweaked drivers I like allot back in the day... These days the bog standard off nvidias site are just fine no need to get tweaked drivers. Quadro is really just the bios in these cards that allow them to be used by some software to accelerate some things they dont allow the gamming varients to do... Drives will not get you around this... You can flash the bios on some cards to make the quadros and vice versa but I would not do that and I would really not do that on a 680...
I just shuddered a little at the thought of someone trying to flash a 680 with the current market shortage.