With absolute expert help from Rahul, I have now managed to solve the issue of IPv6 and ISIS export policies.
We created the pool and prefic on the LNS
We created the PPP IPv6 subscriber interface on the PPP Client
We created the correct routes on the PPP Client
We created the correct high and low prefix on the LNS pool
We created the redistribution of the routes into ISIS on the LNS
It is way too much onformaiton to put all in here, but please PM me if you require the configs we used and explanation.
As I mentioned, Rahul has been superb in this process.