No, unfortunately this is not possible. Unfortunately, the other suppliers block their own apps on third-party Google Boxes... (so that you can rent / buy them from the manufacturer). I therefore have another TV supplier (Zattoo). Double the savings ;-) The Zattoo app can be installed anywhere and is just as good as the one from Swisscom.
I'll put any app on the box for you... no matter which one... no problem... download the app somewhere... Firefox or something... save it on a stick... and install it... allow external installation... username and password, and that works...