Arvid Schneider and Rico Koschmitzky have posted a little tech demo of a new render region tool that will be available soon for Maya. arViewportRender will give you the ability to create a region render directly in Maya’s viewport.
The new Region Render tool will be a great addition for lighting and rendering, making use of the things you can do in the standard render view window, directly in the Maya viewport.
Arvid notes that arViewportRender has been used in two feature film productions so far, with great feedback and will be released some time in early 2015. Looks promising.