QFileDialog::setProxy() can be used to set a custom proxy model on the file dialog:

"Sets the model for the views to the given proxyModel. This is useful if you want to modify the underlying model; for example, to add columns, filter data or add drives."

However, using a proxy model to create a virtual drive entry is not quite trivial. Create an example on how to do this.

Note that an alternative may be to use QFileDialog::setSidebarUrls() to add a virtual drive, and provide a custom file engine for that file.