如何从Dispatcher线程访问单独的线程生成的WPF UI元素？

I need to generate a print preview (a long one) using wpf UI elements like FixedDocument, FlowDocument, PageContent, BlockUIContainer and all those. To keep my UI responsive i'm doing this part on a separate Thread class thread (BackgroundWorker won't work since i need an STA thread). Everything is OK upto this point.I need to generate a print preview (a long one)