feather dusters do use a small amount of CA
to construct their tubes; but they don't require a high level. The level of CA
given from most good salt mixes should be plenty of CA
for a feather duster.
RE placement; I have dozens of small dusters that are growing IN my LR
with small tubes growing out of holes in the rocks. So I think I'd agree with Steve that placement is of little concern other than the cautions Steve also provided.