WiFi connect: Offline-installation possible?

[tiefenauer]

I want to use WiFi Connect in a customized RaspbianOS image. The idea is that WiFi Connect is started automatically on a Raspberry Pi which has not yet been connected to any network. Because the RaspberryPi is offline, I cannot download it from there. So the idea is to have all the files needed for WiFi connect on a host computer, then add them to the image and install WiFi Connect upon first boot. After successful installation, WiFi connect can be run automatically on startup (if WiFi has not been set up yet) by using a bash script or something.

I'm using SDM to customize the image but have not yet found out to do this.