Incremental and permission changes

Hello.

In an installation I manage, there's a NAS with lot of data that is 
backed up with the usual Full/Diff/Inc schedule.
On this NAS it's quite frequent to have sweeping permission changes; 
alas these almost translate an Incremental backup into a Full one.

I don't care about permissions: I can set them up automatically after a 
restore, so I'd like to avoid this.

What's the proper way to tell Bacula NOT to backup a file if only its 
permission changed?
Or, again, don't backup permissions at all, if the above is not feasible?

I also thought about using "accurate: mco1", which should backup the 
permissions, but not the files themself. This could do...
Before putting it into production, though, are there any caveat?

Any other idea?

  bye & Thanks
	av.