In much the same way that we can define a LogFormat for CLF,

LogFormat "%h %l %u %t \"%r\" %>s %b" common

we find the default httpd.conf LogFormat definitions

Replace RefererLog with

LogFormat "%{Referer}i -> %U" referer

Replace AgentLog with

LogFormat "%{User-agent}i" agent

But then we end up with three separate unrelated log files.