Levels stacking for Wild Shape

[Lord Magus]

I am currently converting the 3.5 Arcane Hierophant PrC (from Races of the Wild) as a Mystic Theurge Archetype. The ArHi class levels stack with the Druid class levels for Wild Shape; I have been able to do that by starting with the Shaping Focus feat script.

However, I do not want ArHi to grant wild shape if the character did not have it before getting into the class (for ex: for a Druid level 3). Right now, if I add ArHi levels to a Druid 3, he will get wild shape because of the stacking levels. How can I prevent this?

I have tried
doneif (tagis[Hero.WildShape] = 0)
at the top of the script, but it doesn't work (Pre-levels 5000, like Shaping Focus)

Right now, I use
doneif (#levelcount[Druid] < 4)
but this would not account for Wild Shape being gained through some other mechanism than Druid levels, or for a Druid archetype that would gain Wild Shape earlier than 4th level.

That would sum up to how to script "if the tag is there, but the ability is not enabled, then do nothing" Any ideas???

Thanks!