Ok, after a lot of trials, I did the following, which seems to work.
This is fiddly but, In case anyone is interested...
You need to jar the third party libs. (you will have to edit scripts/bootstrap)
then,
copy all directories under third_party/goog into goog.jar under goog/
Edit goog/deps.js and globally replace "../../third_party/closure/goog/" with the empty string.
This corrects the dependency paths so the third party libs can be found.
That works, as far as I can tell so far
Dave