[Copy&Pasta from another post I did for similar question + extra*]
Hmm... Lets see what I can think of while "away from books"...
1) Possibly, if a team mate or friendly Thieve's Guild has a higher Disguise modifier you can have them try and disguise ya [Aid other bonus?]
2) As stated already, Masterwork Disguise Kit is a sure fire +2 circumstance bonus.
3) I believe that there was a magic item or two that granted Competence bonuses [I believe Mask of Lies MiC book, gave a +5-ish] but most if not all are 'masks' of one form or another. Mask of Lies for example looks like of like a hockey mask imho with crosses as holes for the eyes and mouth.
-Edit-
Mask of Lies [MiC: 4.5k gp/Comp. Adventurer: 17k gp] gives a +5 to Bluff. Silly me...
4) I honestly don't know the answer, but what happens if you Polymorph into a Changeling, and use the Changeling's Alter Self-like ability [its a physical not illusion] ability to change yourself again?
-Edit-
Arc Vembris
Changeling's shapechanging can still be seen through by True Sight. It's a physical tranformation, but TS still shows the changeling's natural form.
5) Along with Second Impression, Assume Quirk [googled to be sure] takes the familiar sights penalty a person gets when trying to see through your disguise. Sadly I think it has a duration/day [1 hour-ish?]
6*)
Dust of Disappearance7*)
Nondetection8*)
Quote:
"The cloak of Khyber spell (Dragon 337) is a 3rd level sor/wiz spell that lasts 1 day/level and renders any illusion/shapechange/disguise magic on the caster impervious to true seeing as long as the disguise is kept up for six or more hours."
-along with-
Quote:
"A more official (and probably more recent) source for the spell is City of Stormreach page 59. [another spell found in City of Stormreach is Animate Infectious Zombie on page 144.]
The internet claims Cloak of Khyber is also found in Mark of Heroes, a softcover module published by WotC for the RPGA."
[Google-fu'd from posts somewhere else on the internet]
9*) Circlet of Persuasion for a +3 Cha check bonus to your Disguise?
10*) Get a way to have a Medusa's Flesh to Stone sight? [not serious, just an idea I had...]
... That's all I got for now...