Then don't ad salt until you taste it.
This might be considered blasphemy in these parts but I always season the Roux itself. I try to keep everything else as bland as possible and then when it all comes together the roux seasons the entire soup. If I need to I can always add salt after. But for this reason I try not to add too much salt to the stock or fat if I don't have to.
I'm sure this all sounds crazy, but hey, I have like a billion posts here. If I haven't sounded crazy by now, it might be about time to start.