Is it possible to have a proof, like a written document, that I am elegible to the 72h Visa?

Hi, I am italian flying from Berlin to HongKong then Taipei then Shanghai then return to Berlin. In Shanghai I am staying only 2 days, so I will apply for the 72h. I want also to apply for the Exempt Entry to Taiwan, which requires :
"...a confirmed return air ticket or an air ticket and an entry permit for the next destination..." At the point of entering Taiwan I will not have the 72h free transit for Shanghai, since I will apply for it when leaving Taiwan. How can I prove to Taiwan, when I enter, that I don't need the entry permit to travel to my next destination (Shanghai)?