Can't set module provider's properties on a project level

I'd like to set the conan.installDirectory on the project level to eliminate the need to do that from the command-line:

Project {
    qbsModuleProviders: ['Qt', 'conan']

    moduleProviders.conan.installDirectory: project.buildDirectory
}

However, this doens't work:

ERROR:

project.qbs:4:42 Item 'moduleProviders.conan' is not declared. Did you forget to add a Depends item? 

It works on a products' level though, but I have too many of them to consider it as a reasonable workaround.