I added about 15 leaderheads to my game by changing the XML - it's the same as with a PC, it's just that the file paths are going to be different. You probably have a Custom Assets folder somewhere on your computer, maybe even like the Documents/CivBTS/ path of the Steam Edition. You need to work from that folder, putting the leaderheads there as well as the custom XML.
If you don't want to mess with XML (the link I included in my last post tells you how) you'll need to load the leaderhead you want as a mod - look for the leaderheads that are 'modular' (a lot of Sabotlieh's are like this). It's a simple process of unzipping and putting the files in the right place. The reason I went the XML route is because I didn't want to have to load a mod for the leaders to be there and I wanted to add too many. From my understanding, you'll need to install one of those leaderhead packs if you want more than one when you use a mod and then you can't really choose who you want. Good luck!