An assembly for use in a late lean injection system of a combustor of a combustion turbine engine, wherein the combustor includes an inner radial wall, which defines a primary combustion chamber downstream of a primary fuel nozzle, and an outer radial wall, which surrounds the inner radial wall forming a flow annulus therebetween, the assembly comprising: a boss rigidly secured to the inner radial wall, the boss being configured to define a hollow passageway through the inner radial wall; a transfer tube slideably engaged within the boss; a stop formed on the transfer tube; and damping means positioned between the boss and the stop.