Hello @Daniel5
Thank you for your query.
The Swiss Half Fare Card can be purchased online on https://www.sbb.ch/en/leisure-holidays/travel-in-switzerland/international-guests/swiss-halffare-car... or at a SBB ticket counter.
At the counter the ticket is printed on security and if you buy it online you can print it yourself.
Since you do not receive a SwissPass, you cannot make the link on the app. However, you can set on the app that you have a Swiss Half Fare Card and thus buy your tickets.
For more questions, our specialists will help you on 0848 44 66 88 (CHF 0.08/min) or by mail to ticketshop@sbb.ch.
I wish you a nice day.
Kind regards, AferditaS