Sorry - today it's not possible to do what you're asking for. My understanding is that we are planning on a solution to this issue, but I don't have a firm time line for it.
Hi Vanesa, we are working on an update to the TOL administrative views which may address your request. If you haven't already, you can add comments or vote up this related idea: https://community.tableau.com/ideas/4750.
Ashley, I've just voted. Thanks!
I hope we can have this solved ASAP.
We understand that the lack of repository access is a huge pain-point for Online customers. Solving this problem is a top priority. The Tableau product team has prioritized this work and is developing a feature that will provide Online site admins with the ability to connect to published datasources that contain their site's repository information. This will allow you to create the custom user activity report you mentioned above. We plan to ship in 2018, but we cannot guarantee a firm date.
In the meantime, we are planning to launch an alpha to a subset of customers. Would you be interested in participating? Please respond to this post and we will add you to the list!
Sure, I would love to participate. Please, add me to the list.