I thought, at first, that you could use s template, but, checking the pre-existing templates, there is no Backup Object Summary
I checked the 'global' file, and saw nothig about this, but, I wouldn't expect there to be anything there, since 'global' is exactly what the name implies, that is, for all systems in the cell, but is mostly for Cell Manager environment variables
Last, I checked the 'omnirc' template. All I found that was even close was
# OB2SKIPDIRECTORY=0|1
# Default: 0
# Setting the variable allows the backup option -skip for directories, not
# only files.
So, if you are aware of an environment variable that will skip a specific file, it is not documented
Some of the other folks who contribute to the forum may have found something useful that pertains to this