He'd said straight off that it had been remapped for the parts. Didn't say whether it was via SERT, download, or some sort of piggyback unit, though. Probably safe to guess it was an ECM download.
You're not suggesting that simply putting a fueler on an otherwise correctly-tune bike (all factory stock or all SE stage 1 parts + download) would increase power production by 8-10 HP, are you?
Might be better to suggest that putting "stage 1" components on the intake/exhaust will net ~ 8 HP increase and changing the fueling and spark timing to match the parts will get you another ~ 2 HP on top of that, while making it all user-friendly and usable.
That's already been done in this case.
If everything else is set up and operating correctly, the only way to get more power now will be to do some work on the engine innards (in conjunction with appropriate tuning changes, of course).
Or maybe it just needs some mufflers with more back-pressure than what he's got now.