How to bypass log 1024 byte limit / truncation

I'm trying to log the content of excessively long Cookie HTTP headers, per the instructions in some questions such as:

• https://devcentral.f5.com/questions/logging-http-header-that-is-longer-than-the-maximum-allowed
• https://devcentral.f5.com/questions/problem-with-irule-that-logs-excessive-http-header-lengths
• https://devcentral.f5.com/questions/log-connections-that-exceed-maximum-header-size

All of these are supposed to log the full content of the header - that's the point of them. But the log command goes through the local syslog-ng, and (per https://devcentral.f5.com/wiki/iRules.log.ashx) truncates messages at 1024 bytes.

I found a few mentions that HSL may not have this limitation, but unfortunately my dev/test load balancer is running 9.4.7, so that's not possible. The production boxes are running 10.1.0, but I'm sort of hesitant to make my first use of HSL without testing it in a safe place.

Is there any way to just dump this to disk somewhere, or any other way to bypass syslog?