Exploit the threaten an area rules
Yes, as noted above.
You can also exploit the rather badly written "threaten an area" rules (which cause flanking) by threatening an area when invisible (but not attacking).
Meaning, you don't have to attack to causing flanking, in fact, strictly according to the rules, you can create flanking while silenced and invisible (if you have a weapon out that threatens the enemy).
Threatening an area does NOT have anything to do with the enemy knowing that something is there... this is the weak rules (as written) part.
Thus, a rogue could get a companion/cohort/etc. whatever that as a standard practice goes invisible at the start of combat and roams around the battlefield never attacking but creating flanking opportunities left and right. Just make sure they can threaten an area, that's the only requirement.
Yes, it's pretty silly, and calls for a house rule at some point, probably, unless you want to allow the enemy to be distracted by something it knows nothing about (i.e. a silenced, invisible, non-attacking but threatening an area ally of the rogue).