With Strangler from ultimate combat, you can cause your sneak attack damage twice per round, once on your regular grapple check (as part of the grapple check), and again using a Swift Action that does not apply any other modifier.
Whenever you successfully maintain a grapple and choose to deal damage, you can spend a swift action to deal your sneak attack damage to the creature you are grappling.
If you are grappling a foe, which also happens to be flanked, you can use your Sneak Attack on your grapple check's free attack.
Once you are grappling an opponent, a successful check allows you to continue grappling the foe, and also allows you to perform one of the following actions (as part of the standard action spent to maintain the grapple):
Damage: You can inflict damage to your target equal to your unarmed strike, a natural attack, or an attack made with armor spikes or a light or one-handed weapon. This damage can be either lethal or nonlethal.
This means that if your sneak attack is 3d6, your will cause weapon damage + 6d6 damage using your standard and swift actions at 5th level.
PS: You can take Dirty Fighting instead of improved unarmed strike as the requeriment to qualify for Strangler.
If you happen to have a friend who also has sneak attack (or simply wants to cause sneak attack damage), both of you can take the Precise Strikes teamwork feat to increase your damage by +1d6. Pack Flanking might also make sneak attacks easier to deliver.
As an alternative, you can look up for an ability similar to Solo Tactics so you won't have to depend on other characters to have the same teamwork feat. The Consigliere rogue archetype from Ultimate Intrigue can do this, but much later (10th level).