I was having the exact same problem, in the exact same IDE.
The solution to this is to download Ukulele from here:
http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=ukelele
In the application you can create a new keylayout using File -> New from current source. Pressing Option will show you in the place for Option-b a red colored key - meaning it's a dead key. Double clicking it will allow you to change it from a dead key to an output key. When prompted for the output you can put in the same thing (by pressing Option-b).
Thus it will output the same character but will not be considered a dead key, so Intellij can bind it as a shortcut.
To enable your new layout you must save it into your ~/Library/Keyboard Layouts (it helps if you give it a new name with Keyboard -> Set Keyboard Name), and then enable it from System Preferences -> Language & Text.
