Access saved credentials from "expressions"

Is there a way to access a saved API key and token via expressions, in the same way that we can access values from other nodes with $node()?

Use case: I want to send a POST to a Trello API that would add an attachment to a card. It uses query params for key and token, which are already saved in the Trello API credentials I have set up. Is there a simple way to access those for situations like this? There are so many endpoints in APIs that it would be unrealistic to have them all within n8n, so this is a workaround idea I’m playing with.

@wilsongoode as far as I know this is yet not possible. I see how that can be handy for some use cases.