Not sure if this is really on topic here, but I'm trying to get the same thing working on pfSense and came across this:
Do a search for "disablesyslogclog"
In theory this will get what you want, but need to be careful of disk space.
I'm going to test tonight. Ideally filebeat would be able to work with the clog setup so you don't ever have to worry bout the space constraint.
I'm going to try and test this out tonight.