Greetings Matt.
There is no canned report in Patch Manager that provides this information, but it is a question we see from time to time, and it's something that can be done. It involves modifying a Managed Computer Inventory task to capture the registry value on the client systems that contains the LastLoggedIn user, and then generating a report from the System Information (Registry) report category.
In fact, we've seen it often enough that we wrote a collection of Knowledge Base articles describing how to it. :-)
How to find the last logged-on user for a managed computer
How to collect managed clients' Registry information
How to configure Inventory tasks to populate Patch Manager reports
To access the data in a report, run the Basic Registry Information report from the Computer (Registry Information) report category, and filter on the appropriate values in the "Registry Value" column. (E.g. on Win2000/XP/2003 systems filter on "DefaultUserName" and "DefaultDomainName" and for Vista and newer systems filter on "LastLoggedOnUser".)