While I wait for UWP support, I got around these build errors by wrapping all my Leap specific code in if defs:
// Leap Code
You can set the Global Symbols in Player Settings to turn it all on and off at once. Then when you do a UWP build, just rename the LeapMotion sdk folder to LeapMotion~ (or .LeapMotion) so it's ignored by Unity.
This allows you to keep building UWP apps without Leap support, but enables you to continue developing in the editor (or shipping your app with Leap support on other platforms).
If you want to automate it more, you can rename the LeapMotion folder in C#, then do an AssetDatabase.Refresh() to reload assets without the Leap data. Then BuildPipeline.BuildPlayer() can be used to build from C#. Then, in C#, put everything back to the way it was before.
There might be a way to use PlayerSettings.SetScriptingDefineSymbolsForGroup to automatically turn off the global script define from C#, but I never figured it out.