Overwrite S3 endpoint using Boto3 configuration file

OVERVIEW:

I'm trying to overwrite certain variables in boto3 using configuration file (~/aws/confg). In my usecase I want to use fakes3 service and send S3 requests to the localhost.

EXAMPLE:

In boto (not boto3), I can create a config in ~/.boto similar to this one:

[s3]
host = localhost
calling_format = boto.s3.connection.OrdinaryCallingFormat

[Boto]
is_secure = False

And client can successfully pick up desired changes and instead of sending traffic to real S3 service, it will send it to the localhost.

>>> import boto
>>> boto.connect_s3()
S3Connection:localhost
>>> 

WHAT I TRIED:

Im trying to achieve similar result using boto3 library. By looking at the source code I found that I can use ~/aws/config location. I've also found an example config in unittests folder of botocore.

I tried to modify config to achieve desired behaviour. But unfortunately it doesn't work.

Here is the config:

[default]
aws_access_key_id = XXXXXXXXX
aws_secret_access_key = YYYYYYYYYYYYYY
region = us-east-1
is_secure = False
s3 =
    host = localhost

QUESTION:

1. How to overwrite clients variables using config file?
2. Where can I find a complete list of allowed variables for the configuration?