That would be OK, just maybe put a small rock in when you can, and if he attaches you could move him when better.
Seriously, best to leave alone as much as possible.
Nems can go a long time w/ out food, in fact when I first got mine I had no idea about spot feeding.
My nems picked up a small amount of mysis for about a year and a half.
LIGHT is their main source of energy more than food IMO