Hello Elisa Clara!  I -think- you can add a little extra baking powder to a recipe in a lot of cases.  I'm going to ask a friend who is also Muslim and see what she does in cases like this, but I wanted to reply so you know your question was seen.  There are some web sites that suggest substitutions, but nothing is as good as someone else who's actually done this sort of thing! 

For now I might suggest making a small batch of the Quick mix without it and see how it bakes up.  Also, a little acid when you use the mix, like lemon juice etc, because cream of tartar adds acid which helps the texture of baked goods.  I'm not sure, but I'll try to find out more.  Thanks for the question, it'll probably help others too.

Edgefield,  It's the byproduct of making wine I believe and so it's not allowed to be consumed.  I'm still waiting to hear from my friend, if I don't hear via e-mail in the next day or so, I'll telephone her.  Suzanne said that it's ok to skip it completely though.