Reporting unique Users in Page-Report?

Hi Piwik-Community,

the standard-report about pages reports the pageviews and the unique pageviews. We want to report the number of unique users that has viewed a specific page. That means even if one user viewed the page today twice and tomorrow again, only one user should be counted. We’re using the setUserId-Property to identfy the user.

I found out in the documentation, that the metric nb_users would be right.
I’ve tried to access the data via the API and found out, that it doesn’t work:
The Request to the API
<result> <nb_pageviews>554</nb_pageviews> <nb_uniq_pageviews>363</nb_uniq_pageviews> </result>

Is there any posibillity to report the unique Users (set via the setUserId-Property) who have viewed a page?

I hope my question is understandable and I’m looking forward for your responses
Kind regards

@thomas_piwik: Do you have any idea how to solve this topic? Have I missunderstood something? Do I need to write a plugin or extend piwik? or is it an unsolvable problem?