A question for you:
Why did you make the graft a couple inches above the roots? There will always be a visible graft scar. The lower trunk is always a primary feature of every bonsai.
Next time, you might consider putting the graft lower, just above the root flair.
Or...
Placing the graft up higher. JBP makes nice bark. Fairly quickly as these things go. So, grafting up higher gives you a JBP trunk, and then the foliage is built out of the scion.
One trick the Japanese do when grafting Japanese White Pine onto JBP and making the high grafts, is to choose a scion that has two twigs. One twig will be the future trunk, and the second will be the first branch. That first branch can then help hide the graft union from view.