Per definition (in RCC tradition) a baptismal Godfather is the designated male figure to take on religious instruction of the child, shall the father becomes unable to fulfill this responsibility due to death or grave injury. Other sacraments do bring their own Godfather figures, which are closer to a mentor/role model (e.g. RCC weddings include the figure of marital Godparents, who ough to be an older, married, couple that should help and advice the newly weds in an impartial way, since their natural parents are most likely to take sides).
Now, the spirit of the oath is not "to raise them as if my own children", but "to raise them, to the best of my ability, as their father/mother would have done". The letter of the oath is to raise them as "good Christians" (i.e. Roman Catholics). Depending on the exact wording of the ritual, there might be some other restrictions as well.
Regarding the original question, it is my opinion that you should consider (to the best of your ability): 1) Is this sort of magic one I would comfortably perform and still call myself an observant Catholic? and 2) Would the deceased parent approve?
Re: Magical Ethics
Now, the spirit of the oath is not "to raise them as if my own children", but "to raise them, to the best of my ability, as their father/mother would have done". The letter of the oath is to raise them as "good Christians" (i.e. Roman Catholics). Depending on the exact wording of the ritual, there might be some other restrictions as well.
Regarding the original question, it is my opinion that you should consider (to the best of your ability): 1) Is this sort of magic one I would comfortably perform and still call myself an observant Catholic? and 2) Would the deceased parent approve?