Will this work...
What you are describing is "fill flash". Every cheap camera I've seen in the last two decades has this capability so I'd be surprised if the nx100 did not support fill flash.
BTW - I'd take any photography advice of the form "Always do XYZ" with a grain of salt, especially this advice about always using flash. Fill flash often improves photos on close subjects in certain lighting conditions, but it isn't a panacea. For example fill flash will just drain your batteries, decrease shot-to-shot time, and increase backscatter when shooting distant landscapes.
|Common Flashwing by digimania|
from canon dslr
|The Marilyn impersonator by Lee8282|
from Blowing in the Wind (Nature)