Disclaimer: I have not used ClamAV. Having said that ...
You should be able to install it during the startup task (with elevated privileges). I looked at the ClamAV wiki and it seems msi has a silent installation:
msiexec /i clamAV.msi /qr
You will need to change this last parameter to / qn to force "no user interface".
. , clamdscan ( ).
, : , MSI (, ).