patch backup files

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

Is there a way of telling patch (or some other equivalent tool) to only
create a backup .orig file if one doesn't already exist?

(The use case is apply two patches which both patch the same file, then
run mkpatches, which only picks up the second patch as the second invocation
of patch changed the .orig file which mkpatches is using as a baseline.)

Cheers,

Patrick