I have built a level editor for an XNA-based Megaman clone I am working on and one of the features I would like to implement is the ability to save a full-resolution map of the entire level (like this one). My problem is that the levels can be arbitrarily large and XNA has a texture size limit of 4028x4028. I don't need to use the texture for anything in the editor itself, only to save it to disk.
I have stored the image data in an array using game.GraphicsDevice.GetBackBufferData, but I am having trouble finding a way to store this to disk in a readable format (preferably PNG). Everything I've found online says to use the Texture2D.SetData and Texture2D.SaveAsPng methods, but those calls are restricted to the 4028x4028 max texture size.
Note: I do realize that the example map I linked above was likely created by hand and while I could certainly output multiple full-resolution images of each screen and put them together by hand in Photoshop, I would like the process to be available directly in the editor if possible.