The flue cannot be moved. Is there a way a way of lessening the visual
(cosmetic) aspect of the pluming so that it doesn't look like a smoking
chimney?

Having previous had an Ideal Icos flued through the wall, I decided to put
by new Greenstar flue through the roof. A smoking chimney effect isn't so
disturbing up there!

I'm not suggesting that the emissions are lessened. I'm thinking,
for example, of putting something around the flue.

Don't do this. A poorly designed flue shroud could cause the boiler to
dangerously malfunction. The main way to reduce plume nuisance are to run a
long flue, so most of the water is expelled already, or to run it to where
it isn't a nuisance, like shoving a vertical terminal out the top of a
unused chimney pot.

Christian.