Since it's guaranteed to trigger from 200 uA, you'd have to limit the current to less than that to have a hope of it not triggering. From a 3.2 V source, we can compute from Ohm's law that R = 3.2 / .0002.
This tells us that if the resistor is 16K ohms (or less), it's guaranteed to trigger. It doesn't tell us just how much less might be needed to dependably prevent triggering though.
There will undoubtedly be some level of current below which it won't trigger. If you want to play around with getting at least some idea of the maximum current that won't trigger, don't play with how many hundreds of kilohms are needed. Work in something like powers of 10. If a hundred kilohms still triggers, try a few meghoms. If that still triggers, try tens of megohoms. If that still triggers, try hundreds of megohms. When you've established some bounds, then you could do something on the order of a binary search to narrow your lower bound.
Then, of course, pad your result by a fair amount anyway--even if (for example) 5 megohms is enough to prevent triggering with the specimen you have at hand, another one might trigger on half that much current...