I am trying o insert a magnet into a few pieces of tyranid biomorphology and was wondering how anyone else does it.

I tried using my drill, then realised that my drill heads are not large enough and my hobby drill can't hold a large enough drill for a magnet.

So how do you guys do it? I've done arms before where i have just cut off the ball and put a magnet with a greenstuffed ball joint in it's place but with things that i can't just cut off (like the adrenaline brain glands) i'm not as sure what do.