Specify signing subkey

[jasonaowen]

On keys with multiple signing subkeys, is there a way to tell vim-gnupg which to sign with?

gpg allows for selecting this with --local-user <subkeyfingerprint>!:

   --local-user name
   -u     Use name as the key to sign with. Note that this option overrides --default-key.

When using gpg an exclamation mark (!) may be appended to force using the specified primary or secondary key and not to try and calculate which primary or secondary key to use.

The exclamation mark syntax works for encryption in vim-gnupg when encrypting to a recipient with multiple encryption subkeys, but I can't tell how to select which subkey to sign with.