Two ways of achieving this. Firstly, you could implement NAC, and force your client to download an app from a web-page. If they install the app and pass the scans, they get access. If they don't install the app, or they fail the scans, they get dropped in to a private (quarantine) VLAN where they can do no harm.
Secondly, you could just present them with an Acceptable Use Policy that they have to accept as part of the authentication process.
Both options will require you to upload a custom web page to the WLC, which isn't too tricky.
Regards,
Richard.