Can I train a network to get the output for the other network?
It surely works, you just don't apply backpropagation to the weights of B.
Let's assume there are two networks called A and B.
I want to train the network A to get the output which is also the input of network B. 
Network B can be considered as a trained network by other people. My work is to train the network A and the weights of network B would be fixed.
Can it work?