We have to go by the letter of the law (regulation) which indicates no added weight. If your entire length of line was lead core then you would not be adding additional weight. If you use a short section as a leader and it has the effect of adding weight it could be viewed as a violation.

Honestly, until you asked I had never heard of this method. But, the internet is a wonderful thing and I quickly learned about it. It seems to be a method used worldwide. If it's something you think should be taken under consideration to be allowed under the regulations I would suggest contacting the Fisheries Division and letting them know. (The more people that contact them the better)