I may be the only geezer left who still rides with bar-ends (bar what? as my local bike-shop punk responded when I asked if they had any), and I'm sure I am not the first person to think of this but it works so well I had to share it.
I use flat bars and I ride with my hands on the bar-ends quite a bit. I can't quite reach my 2-finger brake levers from this position, so I am always switching back to the main bar when I need to shift or slow down. You used to be able to buy these little extensions that mount perpendicular to the ends of the brake levers so that you can reach them from the bar-ends. You might still be able to get them somewhere, but when I was shopping for brake pads for my old beater-bike, I had an 'a-ha' moment. The newer metal-housed V-brake pads are exactly the right shape and size to use as brake lever extensions and they have built-in mounting hardware. $6.50 at MEC and a hole drilled in the end of the lever does the trick.
I am very impressed with how well they work. I can easily reach these from the bar-ends and don't have to change hand position, even for a panic stop. I run hydraulic disk brakes, which require quite low lever force. I don't know if this mod would work as well for cable-actuated brakes. The pictures show the mounting nut on the inside of the lever, which doesn't leave a lot of extra room for your fingers in the normal braking position. I have since reversed the bolts, which works much better.
Mtbr's 2016 Winter Biking GearReviews and Roundups
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Thread: 5-minute brake-lever mod