[NTG-context] active characters in mkiv (and mkii)

Hi all, I would like to make the exclamation mark active within my Greek environment; it should remain a normal letter outside of these commands and environments. (Why? Exclamation marks aren't used in Greek, and in mkii, I had mapped it to the sublinear dot which is used for epigraphical and papyrological texts.) In pdf(e)tex, Hans wrote this macro for me: \long\def\rescanwithsetup#1#2% {{\directsetup{#1}\scantokens{#2\ignorespaces}}} but I'm not sure how to have a similar thing for mkiv (and ! is special anyway, so I'm running into trouble here...). Any pointers? Or is this a bad idea, and I should look for other solutions? Thanks Thomas