Importing IIS logs, 1 log file with both proxied and non-proxied records (x-forwarded-for)

So I am using IIS and using a single IIS Site for an umbraco install, which has multiple sites/domains in the one umbraco installation. Therefore, i have 1 single iis log file per day for the umbraco installation.
Some domains are going through a load balancer and use x-forwarded-for, but other domains in the same log file do not…
If i use mapping in the import_logs ( --w3c-map-field X-Forwarded-For=c-ip ) it works for the records that have X-forwarded-for values, but records that do not get imported with

Does anyone have any advice on how I could use x-forwarded-for only if a value exists or only if the c-ip is in a specific list? or any other ideas?

Thanks in advance.


I’m not too familiar with the topic, so my workaround would be to split the file into subfiles using something like grep and then import every file separately (with the correct command promt).