The later won't work - generally, not just for these addons - as all addons write to a per-account directory (WTF/Account/<gameID>/SavedVariables) or per-character directory (WTF/Account/<gameID>/<character-name>/SavedVariables) and overwrite the file on game exit. This means that although they will start in the same place after the first copy, different games will replace the file and so lose everything but the last game's changes.
Generally speaking, both cross-account data sharing and cross-character data sharing require explicit support from the AddOn. Cross-account data sharing also requires using the game itself as the means of data transfer - think Altoholic or Jamba - as addons cannot write to files outside WTF/Account/<gameID>.
tl;dr - can't be done without bugging Norganna
@Crowdx: yes, you can think of symlinks as shortcuts that work transparently
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