Actually, I think I have a better way of doing what you originally requested.
It turns out that both recipient warning and admin warning in Zimbra are controlled by Zimbra configuration options, called respectively zimbraVirusWarnRecipient and zimbraVirusWarnAdmin. See [SOLVED] Drop virus messages? and Zimbra Attributes ZCS6 - Zimbra :: Wiki
So really all you need to do is (as zimbra user):
Then zmamavisdctl restart.
zmprov mcf zimbraVirusWarnAdmin FALSE
And yes, only the user will be notified, unless you also also change zimbraVirusWarnRecipient.