extending gutenprint paper definitions

[Gary Aitken]

Having gotten cups straightened out (Thanks Tijl),
I need to extend the gutenprint paper options.

In the old version of gutenprint, I did this by modifying the file
  /usr/local/share/gutenprint/5.[x]/xml/papers.xml
and this still works.

However, since that file gets replaced whenever cups is rebuilt,
I'm wondering if there is a better way for an installation to extend
paper definitions.