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Is it possible to change the PASV IP ftp-proxy of OpenBSD sends to clients, without changing the listen address of redirection control (-b <address>)?

I have the following setup:

FTP client --> 1:1 NAT router --> OpenBSD router --> FTP server

The 1:1 NAT router has a NAT rule to forward everything to the OpenBSD router, the OpenBSD router runs the ftp-proxy -R <FTP server IP>. When the FTP client sends the PASV command, the proxy answers with the Entering Passive Mode (227) message with his own source IP on the interface to the 1:1 NAT router (obviously). Since the 1:1 NAT router is not protocol aware, it forwards this message and the client receives the message with the PASV IP of the OpenBSD router, which it does not have a route to.

Is there a way, that I can tell ftp-proxy to send the Entering Passive Mode message with a different source IP?

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man ftp-proxy

-a address
    The proxy will use this as the source address for the control
    connection to a server.
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