I don't know how it's possible with this requirement since bitcoind is a Bitcoin full node.
My understanding so far is that the bitcoin daemon is included in the Core Client and can be started independently of the QT client.
Yes, bitcoind will run independently, and you can communicate with it using RPC or other methods. (
e.g.: bitcoin-cli)
Here's the developers guide for Bitcoin Core:
https://developer.bitcoin.org/devguide/index.html