You could try to add all the needed properties to your gradle.properties file, which you add to version control, but leave the values empty.
Eg:
version=1.0
signing.keyId=
signing.password=
signing.secretKeyRingFile=
sonatypeUsername=
sonatypePassword=
Then you override these in your own ${USER}/.gradle/gradle.properties. As an example take a look at a working project https://github.com/judoole/monitorino. Should be able to run all tasks at any machine except snapshot, stage and build.
Edit: I would not do it like this today. Follow the Gradle guide, using required. Just as the example from @jb-nizet Gradle ref 53.3.3 Conditional Signing: http://www.gradle.org/docs/current/userguide/signing_plugin.html