non-recursive externals

I tried setting an svn:externals property with the following value:

Zend -N
http://framework.zend.com/svn/framework/standard/trunk/library/Zend

- however Subversion complained:

svn: Error parsing svn:externals property on 'lib/vendor': 'Zend -N
http://framework.zend.com/svn/framework/standard/trunk/library/Zend'

This is the project: http://code.google.com/p/qubit-toolkit/

We need some files from the Zend framework, but would rather not have to
recursively check the entire framework.

I was planning to submit a feature request to the Subversion issue
tracker, to support defining non-recursive externals?

Thanks, Jack