Known visitor cookie via API contact creation

Hello,

I understand Eloqua identifies known users by clicking on a tracked link or submitting a web form with the Eloqua tracking code on the page.

We are creating new contacts via API in Eloqua that submit a web form, but since we haven't submitted the data via the web form post submission URL to Eloqua, is there a way for us to make the visitor known if we don't post the data to the Eloqua form because we are sending the data to Eloqua via API post, not the web form action URL?

Is the action URL required to set the first-party cookie in the visitor's browser, or is there a way to set the first-party cookie when creating a new Eloqua contact via API?