Share iTunes library between two accounts on the same computer
I've recently purchased a new Macbook, and while we had one account on the old laptop, I've setup the new computer with accounts for us both. However, having used the same account for years on the old laptop and listening to all the same music, we want to share the same iTunes library and using home sharing isn't a good solution for us. If one of us adds a new album to the library, or updates the metadata I'd like those changes it to automatically show up for the other user.
The standard solution to this problem I've read online (and one that worked for me years ago when I tried it on an old iMac) is to move the iTunes Library to /Users/Shared/iTunes, update the permissions so both users have read / write access, and then select that as the iTunes library for both users.
Doing this _almost_ works, but of one account has iTunes running then trying to open it in the other account leads to a error message stating that the "iTunes Library.itl" file is locked.
I've looked online fairly extensively for a solution to this problem, but the articles I've found seem to reference older versions of Mac OS and iTunes (I'm running iTunes 12 on Mac OS 10.10) and none of them mention the locked "iTunes Library.itl" file problem.
iTunes 12.2.1.16-OTHER, OS X Yosemite (10.10.5)