如何在youtube livestream中使用自定义平板图像?

I am working in a PHP project that needs to integrate Youtube Live events. I need to enable slate in those events and i have implemented it. However, Youtube is inserting its default slate image and i am wondering if i could use my own image as a slate instead.

I have used Control(https://www.googleapis.com/youtube/v3/liveBroadcasts/control) method provided by LiveBroadcasts to enable slate in live events. Following are the parameters that i have sent to the control method together with id of the event.

$part = "status, id, snippet";
$queryPramas = ['displaySlate' => true];

The slate is enabled without any problem. I am just looking for a way to display different image as my project requires me to show a custom image as a way of doing some promotions.

Any help would be highly appreciated. Thank you.

I far as I can see, as per the doc, there are no means to customize the slate image:

YouTube selects the image that displays while the slate is enabled, and the same image displays in all regions and in all video players.

But the same doc specifies that the application developers have complete control on showing ad breaks within broadcasts. As a consequence, for displaying promotional materials, you should use ads instead.