it's not practical. there'll be a problem with batteries. they all draw power from the ipod and often die within 70-80mins (that's when the ipod is fully charged)
on the other hand why not just buy a true digital voice recorder? they are about the same size of the ipod recorder device and definitely do the job better.
the digital voice recorders nowadays generally look pretty much like a normal mp3 player. take, for example, the Sony ICD-U50/60/70.
also note that many Creative mp3 players have recording capability. the Zen Nano is really really very small with capacity of 1GB, more than enough to record all day.