The sorted requirement was added to the presubmit at a time when --vars didn't exist. So the impact on --vars wasn't considered. The sorting had 
two objectives: easier scan-ability of the code (for humans); and 
identifying duplicate entries (human mistakes). 

Trying to keep the vars sorted is leading to workarounds. It will be better to change how presubmit works to remove the sorted requirement, hopefully while keeping the duplicate entry feature.