Configuration for Offline Jenkins Android Gradle Build Server - maven

Question

I have been trying to maintain a build server for my team (Android development) with the following setup:
Windows Server 2008
Jenkins
Gradle plugin for Jenkins
Due to forces out of my control, the server has to be offline. It connects to an offline git repo to fetch our source code. We can get temporary internet access if needed to install updates, but otherwise the machine is offline.
However, it has been working fine for a long time (over a year). The pattern we have been using is that if we change dependencies (such as the SDK, or libraries from jcenter such as 'org.greenrobot:greendao:2.2.1') then we get temporary internet access so Gradle will download the dependencies, and then for future offline builds it uses the cache.
Recently we added a new dependency ('com.commonsware.cwac:merge:1.1.+'), which is not in jcenter, but a maven repo at https://s3.amazonaws.com/repo.commonsware.com.
There seems to be an issue with or config, or with Jenkins that prevents the new repo from being cached.
Here is the relevant snip from our root build.gradle:
buildscript {
repositories {
jcenter()
maven {
url "https://plugins.gradle.org/m2/"
}
}
}
allprojects {
repositories {
jcenter()
maven {
url "https://s3.amazonaws.com/repo.commonsware.com"
}
}
}
Here is a snip from our app build.gradle:
dependencies {
compile 'com.android.support:multidex:1.0.1'
compile fileTree(include: ['*.jar'], dir: 'libs')
compile 'org.greenrobot:greendao:2.2.1'
compile 'com.android.support:appcompat-v7:23.4.0'
compile 'com.android.support:cardview-v7:23.4.0'
compile 'com.android.support:design:23.4.0'
compile 'com.google.android.gms:play-services-location:9.0.0'
compile 'com.commonsware.cwac:merge:1.1.+'
}
When building on Jenkins, if there is internet access the build goes fine.
However, without internet access, it will fail due to the maven repo:
java.net.ConnectException: Connection refused: connect
File C:\Users\ciandroid\.android\repositories.cfg could not be loaded.
Failed to download any source lists!
FAILURE: Build failed with an exception.
* What went wrong:
A problem occurred configuring project ':app'.
> Could not resolve all dependencies for configuration ':app:_debugApkCopy'.
> Could not resolve com.commonsware.cwac:merge:1.1.+.
Required by:
My-App:app:unspecified
> Could not resolve com.commonsware.cwac:merge:1.1.+.
> Failed to list versions for com.commonsware.cwac:merge.
> Unable to load Maven meta-data from https://s3.amazonaws.com/repo.commonsware.com/com/commonsware/cwac/merge/maven-metadata.xml.
> Could not GET 'https://s3.amazonaws.com/repo.commonsware.com/com/commonsware/cwac/merge/maven-metadata.xml'.
> Connect to s3.amazonaws.com:443 [s3.amazonaws.com/52.216.0.27] failed: Connection refused: connect
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
BUILD FAILED
How can I configure it to cache this other repo? What am I missing?