Feats that require ranks in skills.

[Wolf_Larsen]

Feats that require ranks in skills.
I'm trying to create a feat called "Epic Skill Focus". I borrowed coding from "Skill Focus" feat and I can see my new feat in character creation and my new feat lets me pick a skill and adds a bonus to that skill.
However, I don't know how to code the pre-req to Epic Skill Focus that requires the chosen skill to have 20 ranks to begin with.
In other words, before you could apply the Epic Skill Focus feat to a particular skill, that skill would have to have at least 20 ranks in it already.

Ideas?
Thanks, Wolf