IF Mac had a piano roll it would be easy, Select All Notes > Hold Shift and drag one Velocity note up and the will all go up.
Maybe 2017 ???
There are midi plugins that would do it http://www.thepiz.org/plugins put between the midi and SFZ,
but same deal as Win you can't chain them in BB only add an FX after it, you have 1 midi then 4 FX.
The only way to chain them in BB is with MiniHost, load MiniHost in the midi track, load the Velocity normalize plugin, load SFZ.

That's a workaround until something is implemented.