Since this took me over 4 hours to find out after digging through the libicu source code, I thought it'd be a good idea to post it here. do access othere thata than the default "locale" data (which you get by passing NULL as $bundlename), you can use the following somewhat magic strings to get other resource bundles:
ICUDATA-curr
ICUDATA-lang
ICUDATA-region
ICUDATA-zone