I can pop out the standard Blizzard UI to target their corpse (and not have to find their corpse on the ground), but in a 25-man it gets more crowded and annoying. The Druid battle-rez works, but this doesn't. (Or, didn't) I will try it again however... perhaps something has changed in the patches since I last made the attempt.
You don't need to use the default raid frames to target the player, just use the command "target" in the spell slot. On my dk I have it set up so that left clicking vudho targets the player, and right clicking it rezzes them. On my healer I target with shift-alt left click. I know that is not very helpful to your particular problem, but hopefully you can use the info anyway.
I'll do some testing on my lock to see what's going on with the SS. (Edit: I am able to cast Soulstone using vuhdo. Hopefully it will work for you, too. )