Registered specially for you friend.
Was in exact same situation. So what i did (what lead to this situation) - i gave the stones to Emperor, said i would become Illithidh myself, but i didn't. I decided i will do it later.
So you are probably in the same boat.
All you have to do is to have stones in your inventory (main char) AND special tadpole which will make you Illithid.
So you can activate the tadpole (you should do) and can do it even in the fight. What is even more funny - Emperor will say: "rEmEMber yOu hAVe To bE MinD flaYEr to uSE tHE sToNes". No bro, i am not remember this
Wasn't paying attention ffs. Would be nice of you if you remined me like the moment we are at the final door or whatever.
After your transformation you will get this spell immediatly and can finally use it on the crown.
Hope it helps.
