On Thursday, 21 May 2015 14:03:13 UTC+1, Andrew Mawson wrote:
SO - my thought was some form of insulating sausage that I can poke up there
with a long stick - if there was such a thing as a 6" diameter cylindrical
shape I reckon it would stay in place by friction.

You can get jumbo pipe insulation eg

https://www.fluedirect.co.uk/shop/13...for-diameter-6

don't know if that would do on its own or if you could use it as a 'sausage casing' and fill it with a filling of something more compressible.

Owain