[Rosetta] How to perform mass deletion of translations?

Hello,

Short story:
I uploaded the untranslated POT template file over a set of existing PO files, in an attempt to delete the corresponding translations from Rosetta, but it didn't work, and Rosetta failed to import them.
See for example:
https://translations.launchpad.net/openobject-addons/trunk/+imports?field.filter_extension=po&field.filter_status=NEEDS_REVIEW&start=750&batch=75#5189223
at the bottom we have a few import of es_CL.po files, all in "Needs Review" status with "No import target selected yet" messages, even though I only modified files that Rosetta created, so I expected the import path to be wired.
The status page for the imports does not seem to give more info, for example: https://translations.launchpad.net/api/devel/+imports/5189223
How can we accomplish this? (Rosetta's interface does no seem to offer an option to manually reset a term to untranslated).

More context:
Inside OpenERP, we have implemented a fall-back mechanism for country-specific translations, which means that when some translations terms are untranslated in say "Spanish (Chile) (es_CL)", we do use the generic "Spanish (es)" translation instead automatically.
As a result, we tend to ask translators to only ever translate in country-specific languages the terms that are really different from the "canonical" ones (no pun intended ;-)). This makes the set of translations to maintain much smaller for all country-specific languages.
Recently, a new translation team was assigned for es_CL, and they were initially unaware of this system, so started uploading the current es.po files as es_CL.po, to avoid re-translating everything (as Launchpad doesn't seem to support the same concept of fall-back language we have).
Now we would like to cleanup this and remove this identical translations from es_CL, but we can't seem to find a way to do it, as the only option we could find was to force an import of PO files with no translations, and this failed (see above)

I hope this explanation makes sense..
Thanks a lot for you help!