Couple of days ago a Cpt showed me that if you hit LNAV on your base leg (after having extended the centerline and coming out of HDG for a few seconds) you get a pretty good VDI indication (as opposed to what you get in HDG mode after extending the centerline). You still need to factor in your intercept vector, but overall it seems like a pretty good tip. Will try it out a few times and see if I like it.
Cheers
P