Emulating 1-wire device(s)
As far as I know, the 1-wire library you linked in your question allows only to act as a master, not a slave.

I've just released a library to turn an Arduino board into a 1-wire slave, here: https://github.com/neuoy/OneWireArduinoSlave (edit: moved here https://gitea.youb.fr/youen/OneWireArduinoSlave). I use it in my custom home automation system, and it works flawlessly in my setup (the 1-wire master, a DS9490R, is connected to a laptop via USB, and also provides power to the Arduino, which is an Arduino Uno). The library handles low level details: match rom, byte send and receive (which is actually quite hard to get right, mostly impossible without a logic analyzer). The rest is up to you.

It's entirely implemented with interrupts, all communications are performed in background, you can execute other code as usual, in parallel, and are notified by callbacks when bytes are received etc. Sending bytes to the master is also asynchronous.

I also know at least one other library exists, https://github.com/MarkusLange/OneWireSlave, as commented above by Ryu_hayabusa. It didn't work for me (don't know if it's because of my hardware setup or for another reason), but it definitely work for others, so also worth a try. It seems this library is not implemented with interrupts, so your program is blocked while waiting for master activity (which is perfectly acceptable in a lot of scenarios).