I had the Rox 2" on mine and was able to get it to work without extending the brake line. I did re-route the cables to the backside of the triple tree and removed the clamp on the brake line, but it was still a little snug at full lock. I also had to loosely cable tie the brake line in one spot to keep it from catching on something when turning and making it tighter. Mostly what determines how much slack you have is the exact positioning of the bars...both the angle of the risers and how much the bars are rotated up or down in the clamp.
I think the best thing is to replace it with a longer line. If you do keep the existing line, be sure to test it thoroughly to make sure you're not putting undue stress on it.
2014 V-Strom 1000 - Desert Khaki
2011 Burgman 400
2007 Honda Helix
2013 V-Strom 650 - sold