Inspirado no comentário do @KRyan, eu peguei um pouco da parte não humana aasimar :
Non-human aasimars have the same statistics as human aasimars with the exception of size. Thus a halfling aasimar is Small but otherwise possesses the same statistics and abilities as a human aasimar—the difference is purely cosmetic. Non-human aasimars do not possess any of the racial abilities of their base race. However, they are usually raised in the same cultural context as other members of their base race, and thus generally adopt the same fighting style as their peers, use the same types of weapons and armor, and study the same skills.
(ênfase minha)
Adapta-se muito ao que o OP está procurando. Existe uma maneira de um gnomo pegar as Favored Class Options de um aasimar ao invés de si mesmo? Uma maneira de conseguir isso é ser mecanicamente um aasimar e saborosamente um gnomo.
Em bônus, você deve poder usar, com sua corrida de base, o recurso de corrida alterado:
Scion of Humanity Some aasimars’ heavenly ancestry is extremely distant. An aasimar with this racial trait counts as an outsider (native) and a humanoid (human) for any effect related to race, including feat prerequisites and spells that affect humanoids. She can pass for human without using the Disguise skill. This racial trait replaces the Celestial language and alters the native subtype.