GPGme operations with subkeys

[gnupg.20.miller_2555 at spamgourmet.com]

I have a couple encryption subkeys under my primary key. Each key is used for different applications (while I generally just use one subkey, the other is used when a specific application does not permit the use of that subkey).

I would like to select specific subkeys (gpgme_subkey_t) in GPGme to perform operations (eg. gpgme_op_encrypt(...), gpgpme_op_encrypt_sign(...), etc.), but only see a way to pass entire keys (gpgme_key_t) to those functions and rely on gpg to select the key (which does not always select the correct subkey).

I've been through the reference manual (edition 1.9.0, last updated Nov. 2016) and searched around a bit, including the mail list archives, but am I just missing a way to do this or does the functionality not yet exist?

Appreciate the time.