Suggest fieldset, across folders

I have my content split into folders (though thinking this is leading to more troubles than it's worth), blog/2014, blog/2013, etc.

I would like to use the suggest field type when adding new content (http://statamic.com/learn/documentation/fieldtypes/suggest).

I'd like to do this:

  categories:
    display: Categories
    type: suggest
    create: true
    max_items: 3
    taxonomy:
     folder: blog*
     type: categories

but I get an error with the '*'.

Suggestions (besides combining all my content)?