That's still not any better.
If the LLM can run any code it writes itself, it can retrieve those credentials. It's just one `curl` away. If you don't let it run `curl`, but you let it run `python`, it can just run a Python script that fetches it using `requests`. Or a Node script that calls `fetch`.
Point is, if creds are accessible programmatically, the LLM can and may try to retrieve them if it thinks it needs them.
Aws credentials are short lived precisely so that leaking them has a time limited blast radius.
Automatic retrieval, instead of keeping them on disk, is what makes short lived credentials possible.