Pass Analytics visitorID into third party pixel string?

[#1]

Hello, 

What is the proper syntax to populate the Adobe VisitorID into a third party tracking-pixel string?

For example, if the third party pixel were:

<script src="https://analytics-provider/outbound-data-tracking?userID=%placeholder%"></script>

Is there a predefined macro/string that will populate the user ID in place of the %placeholder% above?

Will this work in both Adobe Analytics ID and Adobe Audience Manager, or are there different macros are each?

Thank you!

[#2]

I think that the purpose of doing this is important to answer your question.

Are you trying to map a visitorID of Adobe Analytics to another ID used by 3rd party?  or are you trying to link the ID of 3rd party with Adobe Analytics (or Audience Manager)?