Google Base - how to set the publishing priority?

Hello,

I'd like to set the publishing priority when inserting a data item into an items feed.  The publishing priority is described here:

http://code.google.com/apis/base/starting-out.html#PubPriority

It uses the Metadata namespace ("gm:") to set this.

However, I don't any methods in the Zend_Gdata package to explicitly set this.

Can anyone advise on how to set the publishing priority, either using an existing method, or a way to manually insert a "gm:" attribute into the data item?

Thanks!

-mike