Don't bother buying a longer brake line cable. It's a waste of money. Go to a automotive parts store and buy a short piece of brake line and a coupling. It'll cost you $6 and works great. We did this on my buddy's 06' Crossfire 7. My Switchback needed no extensions with my 5" rise.
I could see your point on a an inverted flare style of hose... but with the polaris...with banjo style fittings on the hoses.... how are you going to couple a banjo fitting on both ends of the line and what auto parts store has banjo fitting style hoses in stock?
Here's mine. 4" Skinz with an 08 D7 riser (which is an 1-1/2" shorter than the D8). I rerouted my brake line, but all is stock. I'm 6'-1" and it is perfect! I love the Skinz bars because they are flat across the top. Much better on the outsides of my palms after a long day. I never sit and it's absolutely perfect for comfort.
Im using the stock dragon riser, with a set of 1 1/8 adaptors and ran a set of pro tapor fat bars(cr Hi) im 6' on the dot and this set up is perfect. a little tall for sitting down but perfect standing up.
i did not have to extend anything, but everything is a little tight. nothing that will hurt the sled tho!