Last logon

I need identify all users that have not logged in within the past 60 days so that we can disable these accounts (it's our corp policy). I know I can use the inactive users report to generate this, but not all logins are captured. I have off-site users that exclusively VPN (using a Cisco client) into our network. They use their domain credentials to authenticate through a RADIUS server. Even though these users login with domain credential they sill show up on the Inactive Users report. Is there a way to capture these logins in the report.

Likewise we have some domain accounts that external users use to exclusively login to SharePoint, but these also are not considered a login by the inactive users report.

Any work arounds for this?