There's a long thread regarding switching over to the daemonized versions of SpamAssassin and ClamAV for efficiency.
Someone has proposed a code change to allow additional arguments to the clamscan command, which will make it possible to call clamdscan instead. Looks like a reasonable wish.
Here's the thread:
http://www.virtualmin.com/forums/message-view?message%5fid=49966
Status:
Closed (fixed)