There is no way to customize the default orientation as far I know (maybe some clever person could write a script and assign it to the numpad keys)
As an alternative you can change the default scene.
Rotate the view to where you need it, then press Ctrl+U to save the startup file. That way blender will always open with your preset view.
Make sure that the Load UI (load User Interface) box is enabled on the user preferences>file>load & save section.
You could also create custom layouts and save those as part of the startup file, that way instead of changing the views, change to the layout that has the orientation you want to use CtrlLeft or CtrlRight
See this related post: Can screen layouts be locked?