My solution:

Order all your future pieces with the front inch or so done in colour 22R and never worry about knots again in your life. When you attach it and cut it in, choose a colour from the Wella Kolesten range that is close to your own, colour all the hair including your own. Et viola, no knots, no hassle with trying to bleach the unbleachable. If you get really close to the base without colouring it you can get the best looking hairline you've ever seen.

Extra bonus of colouring is if anyone ever thinks your hair doesn't quite look right (if you're having a bad day) you can say you colour it and sometimes it comes out a bit strong.