Correct me if I'm wrong, but I believe the switching of bars using a modifier (shift,ctrl,alt) is possible in
Bartender4. You go into the state configuration tab and select what bar you want it to display when a certain modifier is pressed.
So all you have to do is put your abilities onto the bars you want (so sinister strike on bar 1 slot 1 and eviscerate on bar 2 slot 1) and you set bar 1's state configuration to have it switch to bar 2 when shift is pressed.