Runtime undefined reference error when QML plugin uses private API

I am trying to use QQuickDragMimeData as a workaround for this other issue: https://bugreports.qt.io/browse/QTBUG-65183

This is sadly a private API.

I am using CMake as build system and linking my plugin against Qt5::QuickPrivate. However, when running the application that uses the plugin I get the following error:

file:///.../Main.qml:4:1: plugin cannot be loaded for module "MyPlugin": Cannot load library /home/raskolnikov/dev/myplugin.so: (/home/raskolnikov/dev/myplugin.so: undefined symbol: _ZTI18QQuickDragMimeData)

I am really stuck here. The next workaround I can think here is adding a QML DropArea that then forwards events to C++, but that's rather ugly from the client POV.