Follow these steps to get your bulk call data back in gzip form.
First, make your POST call to /bulk/query with your query string. Be sure to add a callback URL or else you will need to refresh the call to see when it is completed.
Next, grab the ID from the response.
Now, when you get notified that the POST call has completed (or you've refreshed and see it's complete), make this call:
curl -X GET \
https://api.openconnectors.us2.ext.hana.ondemand.com/elements/api-v2/hubs/<hub you are using>/bulk/<id from the POST call>/<object you were calling> \
-H 'Accept: text/csv' \
-H 'Accept-Encoding: defate, gzip' \
-H 'Authorization: <Your auth tokens here> \
This will give you back the necessary data in a gzip'ed format.