IAM role switching on an EC2 host without using "source_profile"

I have an EC2 Ubuntu host, where I have a single user account responsible for running different tasks at different times. Each task requires particular permissions represented by a corresponding IAM role (I call them "profile roles"). The idea is to grant this user a permission to assume these roles, when needed.

For now, the ~/.aws/credentials configuration looks as follows:

[default]
aws_access_key_id = XXX
aws_secret_access_key = YYY

[profile1]
role_arn = arn:aws:iam::XXXXXXXXXX:role/role-for-profile1
source_profile = default

[profile2]
role_arn = arn:aws:iam::XXXXXXXXXX:role/role-for-profile2
source_profile = default

...

[profileN]
role_arn = arn:aws:iam::XXXXXXXXXX:role/role-for-profileN
source_profile = default

The user in default profile has a single permission: to assume any role that starts with role-for-profile. The policy JSON looks as follows:

{
  "Version": "2012-10-17",
  "Statement": [
    {
        "Sid": "Stmt1494333413000",
        "Effect": "Allow",
        "Action": [
            "sts:AssumeRole"
        ],
        "Resource": [
            "arn:aws:iam::XXXXXXXXXX:role/role-for-profile*"
        ]
    }
  ]
}

Thus, any application who needs to access specific AWS services in order to perform a specific task (no matter whether it uses AWS CLI, or Boto, or Ansible modules, or whatever) can just specify a profile name and assume the required profile role transparently.

Now my concern is: since this is running on an EC2 host, I don't need to explicitly put any credentials to this host at all. In theory, I could just attach the "master" IAM role directly to the EC2 host instead of creating a user, granting it switching role permission, and explicitly putting its credentials into default profile.

However, I can't seem to do that, as source_profile parameter is mandatory. Does anyone have an idea, how could I authorize the EC2 host assume roles without giving it any credentials? In other words, I want the host to authenticate by principle "something I am" (an EC2 instance with a given IAM role), not "something I know" (explicitly supplied access key and secret key of an IAM user).

UPDATE. Found a couple of feature requests - looks like this is not supported yet :(

• https://github.com/aws/aws-sdk-go/issues/1019
• https://github.com/aws/aws-cli/issues/1390

UPDATE2. It looks like I need to clarify the purpose of this setup. I have different scripts that run on the same hosts (may be even in parallel). Each script requires a specific set of permissions. What I want to achieve, is that each script had only this set of permission, and not more than that. In my view, the best way to achieve this is as follows:

1. On host level provide no permissions at all, except for a permission to assume a number of specific roles.
2. When a script starts working, it needs to assume a corresponding role in order to get required permissions.
3. At the same time, I don't want to bake the role ARN into the script. Instead, I'd like to define a number of profiles in ~/.aws/credentials, each defined to assume a particular role.

I have no problems with the first two items. However, implementing the third one requires me to create a "default" profile that other profiles will use as a reference, and this "default" profile for some reason has to have a user's credentials. What I'd like is to refer to the role attached to the EC2 instance where all this stuff is running.