I think this could be solved using a similar system of auto-success but related to the nurture side of things rather than nature. Imagine if based on training, a character's skill was rated:
• Unfamiliar/Hampered
• Familiar
• Proficient
• Expert
• Specialist
• Master
In this way a ranger who is an expert in Woodlore (that is based on a secondary ability modifer: wisdom) can accomplish many things automatically simply because they are an expert in that field. Likewise for any character who is well-trained but perhaps behind in raw ability, this becomes a method of automatic resolution.
The other feature that I like about this is that it allows you to differentiate between skills that might be heavily skewed to either nature or nurture. For example, jumping is much more related to raw strength and dexterity, with training not having as much influence. Such skills will focus on natural ability scores (rather than training) for automatic resolution bypassing the core mechanic. Alternatively, skills based much more on "nurture" or training such as Arcane Lore, will have training based capacity such as "expert" or "specialist" be what is required for automatic success and resolution. I think this would work rather nicely in representing different skills where as ability score alone fails to represent training heavy skills such as the appraisal of obscure items, disabling traps, the mundane but highly skilled healing of severely injured characters, highly gymnastic manoeuvres and so on.
Best Regards
Herremann the Wise