SFP breakout to another SFP
I would expect that this isn't possible due to the I2C configuration interface and other system status/control signals defined on the connector. You would also need the appropriate power supplies on the board for the modules, so it couldn't be a passive adapter or passthrough board. To coordinate the TX/RX high-speed differential pairs, you would also need to swap pins and likely include DC blocking capacitors on those lines.

What pre-SFP interface are you planning on using? If you are using a consistent optical interface, you could look into short fiber jumpers that have a socket for exposing to the user and use just one (rather than three) SFP on the internal board.