Haven't encountered this unfortunately....my current character is using a 'cursed' sword that has an ego score also but the solution to this would be merely the spell "Remove curse" and ping the sword falls free.....
Now quite sure with artifacts though...my suggestion would be to try this (can't hurt)...and if that doesn't work then either make a pact with another sufficiently evil creature that may be slightly more powerful than your current character...typically swords of this nature will willingly give themselves up for a more powerful owner...then once the sword is passed over get a wizard (in your group hopefully) to dimension door everyone away or just basically have an escape plan and fast....or just "run with it" and play an evil character....sword of KAS is a very powerful artifact and if the wielder works in unison with the sword then you may find yourself killing creatures "above your weight" so to speak (higher CR than the party average)....
Its worth thinking about.
....and to the DM that gave you this item at this low level....I would be very wary now of the adjusted level of your character now that he is wielding a very high level artifact...personally I think he has made an interesting situation but a harder job for himself to calculate the difficulty of any future challenges your party will face due to the sword.....
If I was you on the other hand I would just go with it.....my current character using the cursed longsword is just "rolling with the puches" and making the best of it and making it work for my character...sometimes it just means thinking a little more outside the square.
