For now there are no way to install clean build of MacOS Mojave if you are not under beta developer Apple program but we have a chance to switch default update Chanel to developer version.
All you need is a MacOS Developer Beta Access Utility attached this post and updated latest Clover EFI build with all needed for you system kexts placed on Other directory.
For example I use ASUS K541UV based Hackintosh to install Mac OS Mojave 10.14 over pre installed Mac OS High Sierra 10.13.
Run package file from attached dmg and wait until execution ends. Then in opened AppStore window thats should be show MacOS Mojave download section press download...