When you say glacial, do you specifically mean the whole world is ice or can we see freezing mountains and blizzard covered plains and stuff, too?
If it's the former you want, simply constrict the elevation parameters to < 100. You're not likely to see civilizations in this sort of form, so you should probably set the parameters to continue without playable civs. You'll also want to remove any minimum/maximum/desired parameters for terrain types (so you don't have to keep telling it to allow each rejection type.)
If (more likely) it's the latter you want, simply set the temperature to something like -1000 to 60 (or, as uncool posted, -25 to 25 works; they don't differ all that much.) Since adjacent tiles are within a region subdivision are constrained by the temperature of their neighboring tiles, this number's only really important for the initial seeding of a region (meaning my numbers strongly favor oppressive cold relative to the absolute Ursts temperature scale, while providing in very rare instances, a little oasis of tolerable temperature.) Uncools should provide more variety between the subregions, but not have the possibility of rare oddities. At least, I think that's how the worldgen works. It has been quite a while since I really tinkered with the extremes.
EDIT: Err, did I miss something? Is this thread the continuation of another one or something?