You're aware of the fact that as long as you know what the thread pitch on the bolt is that you can just buy one with a hex / philips / security / whatever head, right? Pull the bolt (try and remember where all the various springs, washers, etc. landed when you pulled the bolt out) and take it down to your local Fastenal / OSSCO bolt / whatever and just get a replacement with whatever head strikes your fancy (if it's pan head or flat head you may have some issues getting a hex head bolt to fit because of the inside taper).
Or, if you have a thread pitch gauge, you could open your McMaster-Carr catalog and order it from them.
Of course, without knowing the exact alloy the bolts are made of you're probably voiding any manufacturer's warranty by replacing a functional section of the brakes. But, hey - if your brakes fail you could always just ram into a tree head first, right? That'll stop you.
I, too, am curious as to why you're adverse to an allen head - the hex shape creates a better (more points of contact) grip and it's a standard tool. They're easy to toss into your saddle pouch or pocket of a bike jersy, too. And it's a lot easier to torque them down to a manufacturer's specification than a philips head is.