Some say vitamin B1 (thiamin) is supposed to help for transplant shock. Thiamin contains sulfur; so, maybe that has something to do with it. If sulfur has anything to do with it, Epsom salt (magnesium sulfate) may help. Peppers are supposed to appreciate a certain amount of Epsom salt (diluted a lot, of course). After googling it, I see a recommendation for Epsom salt with transplant shock (after transplanting).
I have a suspicion that water with a little food grade hydrogen peroxide in it may help (the non-food-grade kind may contain harmful stabilizers, such as organophosphates and heavy metals). Hydrogen peroxide is supposed to help sick plants and roots (and even leaves, if you spray it). So, it may help with transplant shock, too.
One thing I've found is that some plants when they're first transplanted, don't like direct sun. Don't ask me why. They wilt in it, but are fine in the shade. I don't know if this is true for all plants. After one to three days this probably won't matter as much. Your peppers have been planted a while now. So, sun might be a good idea.
Make sure they're warm enough (especially the soil) and have enough sunlight (I'm sure a grow light would help enormously if they're indoors). Make sure you don't overwater them.