Using ssh-agent with encrypted knife client key

It is possible to use ssh-agent with encrypted knife client key.

For example:

I create a user and get it user.pem.
Next I encrypt it with ssl, like:

user="skubriev"; openssl rsa -aes256 -in ~/.chef/$user.key -out ~/.chef/$user.key

And knife client list began to ask passphrase:

knife client list
Enter PEM pass phrase:

But I want that knife will ask a key from ssh-agent, like standart ssh client.

It is possible now ?