I think there's a few widgets that are trying to get the disable 4G capability working, but I haven't really seen any =/
On a more positive note, your friend shouldn't need to turn off 4G as the phone has quite a decent battery life completely stock. If it's still rather new and has only gone through a few charge cycles, I would highly recommend calibrating the battery meter by following these steps:
http://forum.xda-dev...ad.php?t=765656
The OS learns the battery capacity over time, but until it gets the capacity right the phone will often times report that it's out of battery when it's not. This functionality is the reason you'll sometimes here people say their phones have gotten better battery life after a few charge cycles. It's not the battery changing, it's the OS adjusting the battery meter. Following these steps effectively shortcuts the "learning process".
If your friend values battery life, I recommend picking up the HTC Evo 3d battery for $30 since it's compatible with the HTC Sensation and has a larger capacity (1730mAh vs 1520mAh stock).
I've also gone ahead and rooted my phone and loaded a custom rom; after doing all of the above I've netted a significant increase in battery life (rooting the phone also improved the general performance feel of the phone, which I didn't expect, to be honest)