Before Squirrel came to electron-builder I was about to file a PR concerning not having to sign the uninstaller after doing a windows installation etc. I don't still have the code but the idea was to create the uninstaller as a normal program sign it and then pack it along with the installer.
This way the installer becomes somewhat bigger but then one can build the installer without using Windows. The idea was based on http://nsis.sourceforge.net/Signing_an_Uninstaller which as it is would speed up the build process on a Windows machine.