This is my XSI Plugin called 'Nyu Camera', which is standing for 'New Camera'.

It creates a new camera from any viewport, or any existing camera, with having the same settings of the original viewport (pos/rot/height/width/FOV,etc). That means you can create a camera from user view or non-perspective view (right/top/front, etc) which can be used for rendering.

After installing the addon you can find '乳カメラ' command under the camera menus for each viewport. Just select the menu and the camera will be created.

Demo video is narrated in Japanese but it's pretty straight forward plugin so you can easily get the idea and how to use it, I hope.

Download page:
homepage3.nifty.com/jjj/XSIFiles/Plugin/General/NyuCamera/NyuCamera.html