I've seen a lot of people that have just a black (or color matched) piece that goes over where the side marker goes. Dunno where to get it... or what its called though :
most ppls opt to get JDM solid mouldings to replace the side markers....u can order them from any local toyota dealership...i got mine from www.partznet.com
they cost around 100 usd for a pair......or u can simply paint over the side markers as a cheaper alternative.....
clear corners are just the replacements for the amber ones.....not for the side markers.....those are a seperate piece....u are correct when u say its just a piece of the corner assembly.....