Exposure Lock Button X-E1

I have looked through the manual and I can't seem how to truly lock the exposure without holding down the AE-L button. I want to lock onto an exposure, recompose, then shoot and  having to hold down the shutter or the AE-L button is a pain.

On the NEX5n, I can lock onto an exposure and it will keep the lock exposure until I otherwise unclick the option. I don't constantly have to hold a shutter halfway down or hold any other buttons to achieve a lock. What am I missing here?

Thanks in advance.

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_DDriver
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