when using gpg with a smartcard, I need to place a special secret keyring that does not contain actual keys on the machines I want to use the smartcard on. Exporting the secret key with --export-secret-subkeys will give me a key with a stub master key, but with all my subkeys, including functional ones.
It is possible to remove the functional keys using gpgsplit, however having a --export-secret-stubs (or similar) function that would export a dummy master key and all divert-to-card or otherwise unusable subkeys would be neat.
1.4.1 automagically creates the required stubs when doing a --card-status or --card-edit. Merging new subkeys into an existing key does however not yet work. We might do this later. The change is already in the CVS.