Not to state the obvious, but why not just get a new spring from BUSA? The 92D main spring is a little lighter than the 92FS one, enough to make the DA pull smoother, it costs $3-$4 including shipping, and takes about 5 minutes to replace.
That said, I had the opportunity to shoot a couple of Berettas with LTT action jobs this past weekend. I'd say the improvement was surprising. Ernest does great work.