I wanted to do the same thing but ended up needing the multiplatform support, so this approach wouldn't work for me.
I just implemented this which seems to work, I will keep you guys posted if there's anything else to know.
I wanted all WWise editor and source files (including .wmu, .wproj, and the gigs of source .wav files) to live outside the Unity project, except for soundbanks, so that non-sound developers didn't have to see them. I did NOT want soundbanks to live in the Assets/StreamingAssets/ folder, because it would have added all platforms (Mac/Windows/other) into all builds, wasting space. The WWise build scripts are already setup, during builds, to temporarily copy only the platform (i.e. windows) you are actually building into StreamingAssets.
1) I created a new folder, arbitrarily named 'WwiseGeneratedSoundbanks' in the top-level Unity root (next to the Assets folder). This gets checked into source control, and is generated manually by people working in the WWise editor (someday, maybe generated via build machine as well). Everyone on the team gets this file when they sync the Unity folder in source control.
2) I set the WWise editor to generate to this folder in Project Settings
3) I had to modify the WWise Unity build script to hardcode this folder path (this is a bit klunkier than I like, but it works). This is only needed for users that won't have the .wproj file available (i.e. you will need it for the rest of your team)
In AkBasePathGetter.cs, add this on (as of 3/15/2019 with WWise 2018.5) line 145, after the first try/catch and before if (string.IsNullOrEmpty(SoundBankDest))
if (string.IsNullOrEmpty(SoundBankDest))
{
const string hardcodedNonstandardPath = "../WwiseGeneratedSoundbanks/";
var sourceSoundBankPath = hardcodedNonstandardPath + platformName;
SoundBankDest = AkUtilities.GetFullPath(UnityEngine.Application.dataPath, sourceSoundBankPath);
}4) in Unity, Edit -> WWise settings and fix the location of the .wproj file (same thing as editing <WwiseProjectPath> in WWiseSettings.xml file)
Note: this will disable the WWise picker and maybe other audio functionality for non-sound users who don't have the .wproj file, so your mileage may vary. It will probably also disable building of WWise soundbanks from inside Unity, if that's important to your workflow, you probably can't move the WWise editor files outside the Unity project. Also, not sure what happens if you try and reference WWise project elements (like events) from WWise Unity components. This game happens to not need this functionality, so it works for me.
If you're using perforce, getting this going for the first time might be a little painful to make perforce happy. You may have to create some of the directories by hand the first time.
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I hope that helped. It would be cool if this was a more supported workflow out of the box, and if WWise's build scripts played nicer with perforce out of the box as well.
If this doesn't end up working for us in the long-term, I'd suggest (if using Perforce) doing some client-spec mapping to put the gigs of source .wav files somewhere else, while still keeping the rest of the WWise editor files available for use by non-sound designers/coders.
shameless plug: If anyone needs any help with this, my shop does technical consulting for WWise projects, hit us up http://audiotankstudios.com
