ESET as the real time protection module. I suggest using MBAM as a on demand scan, no active real time protection on it. I would disable Windows Defender for improved system performance, windows firewall is controlled by ESET as soon as you install it. EMET would be optional, but won't do any harm.
I recommend that he installs ESET Smart Security on his computer, using ESET for the real-time protection. Smart Security also includes other packed features which will be good for protection like the Firewall (to stop hacker attacks), Botnet protection; more information can be found here: http://www.eset.co.uk/Home/Smart-Security
Like @darko999 suggested, he could use Malwarebytes Anti-Malware on-demand. If, he has Malwarebytes premium, he can disable the Real-time guard to prevent it scanning real-time for threats, and using it as on-demand only.
ESET Smart Security and Malwarebytes Anti-Malware should be enough; I do not think that Windows Defender would be necessary, especially when you are using ESET for example. This can be disabled.
I think you've misunderstood. On-demand is where you do not use Real-Time protection, however the scanning function of the product. For example, the user can use ESET for real-time protection and can also scan the system using Malwarebytes to check if it picks anything malicious up. (threat scan in Malwarebytes for example).
If he has MBAM (Premium even better) with Windows defender/firewall, he only needs a common sense and UAC with it. But, if he has no clue about internet/files treats, he may as well install any premium suite and still be unprotected . At the end of the day, use your spare time to learn.