So, I hung around the station asking everyone who came in if they could please give me change for the 100 lira. Nobody would help. Even the security/police guy at the turnstiles wouldn't help. Finally, a nice guy beckoned me over to the turnstiles and gave me - for free, although I offered to pay - his almost-empty reloadable farecard. Even though the fare machine wouldn't take 100 lira to pay for 2x 50 lira cards, it did let me use a 100 lira note to add value to the reloadable card.