OAuth Scope and Service Account Role

Hello,
we are trying to use that plugin to checkout sources from Google Cloud Repositories with GCE instances. Our instances have a Service Account attached that has the permission to check out repositories.
When to manually configure the according Git credential helper for the Jenkins user, the checkout of our sources works without specifying credentials. Unfortunately this is not following Jenkins best-practices as they recommend to not configure any credential helper and use Jenkins credentials instead.
By working scopes as this plugin suggests, we cannot use a custom service account.
Would it be possible to develop the plugin in a way that takes both cases into account:
- Default Service Account with attached Scope
- Custom Service Account with attached Permissions

Thanks
Eric