This was not easy for me for some reason. This method finally worked (similar to Steve Dignan's answer above but I don't have enough rep to comment yet).
In VS 2012, Tools, Options, Environment, Keyboard.
"Apply the following additional keyboard scheme" set to "Visual C# 2005".
"Use new shortcut in" set to 'Global'.
Enter "splitpane" in "Show commands containing" to get only the 2 desired commands.
Select the first one and remove any shortcuts already assigned.
Click inside the "Press shortcut keys" box and use "Ctrl + Alt + Up Arrow" for prev and down arrow for next.
If either of those shortcut chords are currently used by something else, you may need to search on that command and remove it from there. Then come back to the split pane commands and Assign.
Don't forget to close VS before you open another instance of it.