Use Mini Tool Partition Home Edition Free and make a EXT4 partition on SD where the data will be moved. Now I don't know how it will work on Z1 but this is how it work on HD2, EXT4 will be used instead of Internal Storage. Let me know how it goes, I want do that too.
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My Evolution: Sony Xperia Z1 - UB + 4.3 Rooted + Deodexed, HTC HD2, HTC Diamond 2, HTC HD Blackstone, Nokia 7070 Prism, Qtek 9100, Nokia 3100, Motorola T720i, Nokia 3310, Sony Ericson PF 768 (Blue)