In answer to my own question, in case anyone else has similiar difficulties, it seems I was using node incorrectly.
The API documentation states:
A Node is a named logical grouping of data in the JBoss Cache. A node should be used to contain data for a single data record, for example information about a particular person or account.
Once my cache was structured along these lines, putForExternalRead did what I required.
I couldn't find this information anywhere in the User Guide. Perhaps that paragraph inserted at the start of the User API chapter would help put the rest into context.
Good point. Thanks for letting me know.