I just use Splenda to replace the sugar, and I also reduce it a little bit - using the pumpkin pie recipe on the Libby cans. I also up the cinnamon a bit because it's not enough, per the recipe. I can tell when the mixture smells just right.
The amount of Splenda that is split between all the servings of two whole pies is not enough to make 99% of people have any problem.
If somebody has extreme problems with sugar substitutes, however, maybe they should either use sugar or just not eat this dish. 
ETA - if you want some sugar you can do half and half with sugar and sugar substitute. I like it with all Splenda, though.