Old post, new answer:

You can do exactly what you are asking (understanding the latency element of GCS buckets).

1 - Mount the GCS bucket as a volume with gcsfuse

https://cloud.google.com/storage/docs/cloud-storage-fuse/overview

2 - Set that mounted volume path as a git remote (yes a local directory can be a git remote from another directory on the same machine

How to add a local repo and treat it as a remote repo