Yeah it certainly seems like an easy thing to accomplish. I was just concerned about them allowing enough slack. At what size lift are brakeline extensions no longer practical? 3.5 inches, 4.0?
Disconnect your Jeep and find a dirt mount or something to flex your suspension on so you can see how much slack you have or don't have.
A 2007- 2009 will have less than the the 2010 + because the lines are a little longer if you unbolt them from the spring perch, but then you've got a metal bracket clanking around down there.
This isn't something I would jerry rig and try to circumvent on more than 2.5" of lift personally. For $135 (+4" Crown Performance braided lines) you've got piece of mind that you're not going to lose your brakes on the trail and ruin a few folks days including your own.
Also take into consideration that some 2.5 coil lifts will give you more height on your two door than a JKU. I found the lines to be mandatory on ours with the 2.5 Rock Krawler.
Go test it, take some measurements, and decide from there. Every Jeep is a little different, there isn't an answer book for some of this stuff.
Marcus