SSH from A through B to C, using private key on B

[ghostiam]

    ssh       ssh
A ------> B ------> C
    ^          ^
 using A's   using B's
 ssh key     ssh key

Is this possible with "assh"? https://serverfault.com/questions/337274/ssh-from-a-through-b-to-c-using-private-key-on-b

Commands from the answer do not work with "assh".