How to force Mobile Network over Wifi?

Hello everyone, I'm developing an Application where the Smartphone will be connected in a Local Wifi without internet access and I need to make a http request using the mobile network.

I'm using the https://github.com/SimonSimCity/Xamarin-CrossDownloadManager library to make download via http request.

            var downloadManager = CrossDownloadManager.Current;
            var file = downloadManager.CreateDownloadFile(fileName);
            bool mobileNetworkAllowed = true;
            downloadManager.Start(file, mobileNetworkAllowed);

Is there any way I can force the request to use the mobile network? The flag that I'm using is allowing but is not giving priority too mobilenetwork