We used the attack roll idea last night: d20 + 1/2 cleric level + CHR modifier verses the undead's TC (turning class for lack of a better term) of HD + WIS/CHR modifier (if any) + turn resistance, inflicting 1d6 hp per level of cleric to all within a 60' diameter burst. The attack roll and the TC seem to be fine, the damage however, seems a bit excessive. I would recommend the 2d6 + Cleric level + CHR modifier for damage. I also ruled that a crit would repel those effected for a 10 round duration. The party like this optional method more than those of the core rules. Strangely enough (though it worked in their favor last night) they believe that the d6 per level damage was too much as well (in one encounter, all 8 shadows were obliterated by a 5th level cleric).
I haven't messed with feats or other abilities yet, but I am sure a simple method can be found.
Game well.