I want to prevent all those 408's from showing up in one of my log files. Is there a way to prevent this? I found the syntax for limiting the printing of any particular format string, but not the entire log entry.
Check out conditional logging in apache. I am not sure it will work here unless you can filter on the URI.
Search for Conditional Logging.
Otherwise, look into piped logging. You can pipe your logs into a filter (grep -v " 408 ") before dumping it into a file.
May want to check on any performance hit.