I've never tried that, but my instinct is that you're not going to gain anything versus adding it before primary. Dissolving the stuff cold is a right pain in the ass at any rate.
My technique is to add the stuff after flame-out, immediately before whirlpooling and cooling. Reason being the heat and whirlpool dissolves it perfectly, and you don't steep it for long enough to lose significant flavour/aroma.