Currently there are few ways to raise one's Disguise skill, making it balanced very much in favor of the spotter. Additionally, many methods only work on oneself, which creates an odd situation where a PC can be a "disguise expert" but unable to help anyone around them pull off a look. Imagine if a PC who is an expert in Disguise can provide, using a Disguise Kit, a little of their expertise to other PCs, helping them with makeup, clothing, etc.
It could work in a manner similar to lockpicks and healing kits--better disguise kits providing better bonuses, up to a certain amount and requiring a certain amount of skill on the part of the PC providing the assist. The duration would be limited, of course.