The I2C ports on the BB only support master or slave. Perhaps you could configure one of the BB I2C ports in slave mode and have it respond to your devices that are operating in multi-master mode. I’m not sure how the BB I2C port will respond to bus contentions if two of the multi-masters drive the bus simultaneously though.
Another option might be to have the BB act as the master of your devices as slaves, but each device is connected to the BB via an interrupt pin. You could have interrupt routines that that queue up I2C reads to the appropriate device(s).
Hope that helps,