Dude just get the Lo. At 5'4" your shoulders probably aren't much wider than 14 inches anyways, you really don't need wide bars.
im 5'4" my shoulders are 17, i ride 18 wide i recommend the hi and just cut it down to your specifications because you have the tools and you dont have as much control with 14 wide as you do with 18 or 16 or 17 or watever
For riding park and airs and stuff I totally agree. But he's a beginner, I guarantee it will be easier for him to progress with narrower bars as well as there being a lot of room for error when cutting bars and stuff.