@TomG
would it not be possible to add something like "save to CXR" to the (corona) render settings,
and then use the settings in the normal save dialog? (including support for filename tokens)
this way you'd get the normal jpg/png/exr plus the cxr.
if checked, the cxr saving would take place even if save is disabled in the render settings.
like this you could save the cxr only.
not really the most elegant solution, but a workaround most could live with, i guess.
(if it is not possible to add cxr as normal saveable format)
best, index