How to build NativeScript project for IOS on Windows?
Nativescript-sidekick will do it for you on the cloud ... and for free.
With NativeScript Sidekick you can leave SDK management to us, literally. You simply tell Sidekick to build your app in our cloud and we will deliver you the IPA and/or APK app package back to you. Your NativeScript assets are secure in their delivery to our cloud servers.
As XCode can't be run on Windows and you don't want to virtualize, you have one option left, you can let someone else do the builds for you. For NativeScript, you can get a seamless experience with the Telerik Platform: http://www.telerik.com/platform#overview
There are of course many other mac cloud services (such as CloudBees, MacinCloud, MacBuildServer, Unity Cloud and many others). However, for NativeScript, I'd strongly suggest looking at the Telerik Platform as it's a tool made just for that.