Master tempo adjustment / edit multiple tempo changes at once

It's pretty common for me to work with a songwriter on a tempo map before having a drummer come in and play to it. There's not much worse than having that drummer show up and insist the whole thing is slightly off. There's often no alternative but to redo much of the tempo map, even if you've got some very carefully crafted tempo curves that are brilliantly dead on. I would like to maintain the shape of the tempo automation but move it vertically, like I can with regular automation.
Anything that would alter every tempo change equally with one schwack would do the trick. Drummer says it's too slow? Add 2bpm to the whole thing and move on.
 
Thanks much
-A