Software Deployment

I have a requirement where when I uninstall my MSI, one DLL gets left behind. This is because that DLL is being used by explorer.exe. I came to know this because if you end the explorer.exe and then manually delete the DLL it gets deleted. Since as per my customer I cannot kill the explorer.exe task during install and again restart it after the DLL is deleted (moreover this will create problems in system account, because the explorer.exe will open for the System user), so I wrote something like an active setup that will delete this DLL during Logon after reboot.

But in Windows 7, to remove any file/folder from C:\program Files, admin access prompt will be required, which is not the case on XP. Is there any way, we can have a program run as system context during logon using the functionality of Active setup.

In a nutshell, my problem is simple. I want to run something the first time any user logs on, but to run with Admin/System rights. Can we do it on Win 7?