Rather than an item, I was thinking of researching a spell...+10 insight bonus on any one skill, 12-hour duration. This will prove much more useful in future than a one-shot item, or even a permanent item keyed to Disguise. Such a spell may already exist somewhere, but I can't think of anything Core.
Since the Simulacrum spell describes the requirement as a straight skill roll, I'd assume that anything that could enhance a normal Disguise check will help the check made for a simulacrum. Aid Another would help, but I agree the "other" would have to be there for the whole process. Masterwork sculpting toolsor a masterwork disguise kit might work for a +2 bonus, as well. Stuff like the Skill Focus feat would apply, too, but are hardly worth taking for this reason alone.
So that gives us +2 for having help, +2 for masterwork tools, let's throw in a Persistant Eagle's Spleandor for another +2. If I can get away with the +10 spell or item, that's a +16 to my disguise check, with no CHA bonus or skill ranks. That's not shabby at all, and would be more than enough to fool a casual observer.
Any other tricky ways to tack on a bonus to that disguise roll?