I would also spend about $20 and get a stem riser(Diamond too. It will change your riding posture(more upright) and puts less strain on your hands/wrists/back/legs. It feels nicer to ride now and if your friend has a good sized/big stomach then his legs might hit him in the stomach in the typical mtb bike riding position and this will help with that too.. Also get a nice seat as stock wont be comfortable for long I'd imagine. I started at around 330 and yeah stock seats suck lol but I'm not willing to shell out money for a brooks saddle until I upgrade to a better bike(current ride is a surprisingly tough sams club fs bike plan on getting a ht/rigid soonish) and lose some weight too but back to theseat I purchased a Sunlife Cloud 9 and while it's low end its nice and now my rear doesnt hurt at all on my rides anymore. For 40 bucks you cant go wrong as the only pain you should be feeling now is the burning of working your musles.
Links:
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1