Fails to download libopenh264 when installing offline from flatpak create-usb

When using flatpak create-usb to create a portable version of this extension it will not install on an offline machine as it still wants to download from cisco over the internet:

# flatpak install -y flathub runtime/org.freedesktop.Platform.openh264/x86_64/19.08
Looking for matches…

        ID                                         Arch           Branch         Remote          Download
 1. [✗] org.freedesktop.Platform.openh264          x86_64         19.08          flathub         593.6 kB / 423 bytes

Error: While downloading https://github.com/cisco/openh264/releases/download/v2.0.0/libopenh264-2.0.0-linux64.5.so.bz2: Error resolving “github.com”: Name or service not known
error: Failed to install org.freedesktop.Platform.openh264: While downloading https://github.com/cisco/openh264/releases/download/v2.0.0/libopenh264-2.0.0-linux64.5.so.bz2: Error resolving “github.com”: Name or service not known

I can think of two ways to address this:

• Fool the offline machine into thinking it has the file already when it tries the URL. I guess I can use squid to intercept the request and deliver the file from a cache. Or is there some other dir/cache it will look first? From what I understand it is BuildStream which is being used so perhaps there is a way to point that at a local version/mirror of the file? Any help to find simple solution here appreciated.
• When flatpak create-usb is run against this extension it also includes the cisco file(s). Perhaps though there are legal reasons that the cisco part cannot be included and must always be obtained by an end-user themselves?

Thanks for any help