This thread inspired me to try making my own pretzels to brew with. Following the advice of the first online recipe I found for hard pretzels, I made "baked baking soda" (Na2CO3) for the caustic bath. This turned out way too strong and the pretzels ended up very bitter/soapy.
In a last ditch attempt to save them, I used a lemon juice/cream of tartar solution to neutralize my pretzels (yes, they fizzed!) and then washed and rebaked them at low heat. Now they taste much better, but I will probably use a healthy helping of acidulated malt when I mash them.