Implement UI for hiding sheet. The sheets can be visible, hidden, or very hidden (could be made visible only from the API).

Note: This is already supported on model level (in RadSpreadProcessing).

The control should be customizable so you can place also a content different than an image as in the WPF native splash screen support (https://docs.microsoft.com/en-us/dotnet/framework/wpf/app-development/how-to-add-a-splash-screen-to-a-wpf-application).