Setting skill point cost per level not tied to base cost

[Lavendarjosh]

I've searched far and wide but haven't found an answer or example where this is done.

How do I define a skill point cost for a perk or attribute that is not tied to the base_skill_point_cost? Or is base_skill_point_cost + cost_multiplier_per_level really the only possible way to do this? Because that would be terribly inconvenient. What I want to achieve is tying the point cost the the perk level (lvl1 costs 1 point, 2 for 2 etc.) or just assign cost values as I see fit.