I've found a tricky workaround.
Tested on Windows 7 - Xperia M2 D2306 - KitKat 4.4.4
1- Turn on USB debugging:
Go to Settings > developer options > USB debugging.
If you don't have developer options:
Go to Settings > about phone > press on the build number a couple of times until it says 'you are now a developer'.
2- Mark the Install Software checkbox on USB options:
USB Connectivity > Install Software > Mark the checkbox
3- Connect the USB cable to the phone and computer.
This will try to install an "android" new usb device, but Windows will not recognize it.
(This device needs the Developer Driver, but we don't need it, fortunately).
* No mass storage device nor battery charging yet.
4- Mark the USB tethering checkbox (Sharing your mobile data connection).
Go to Settings > More… > Tethering & portable hotspot > USB tethering > Mark the checkbox.
* An USB icon will be displayed in the status bar and the battery should be charging now.
* No mass storage yet.
5- Then open the Notification panel (To see the USB icon option).
Tap on Install Software.
* This will mount a virtual CD-ROM
* and the Mass Storage will be available (Internal and SD Card).
6- Then you can browse your files in the Windows File Explorer.
I've tested with and without PC Companion.
To use PC Companion, open it before Step 4 and try to pair the phone, this will fail, let the pairing error open.
After Step 4 and 5, PC Companion will pair the phone.
Then you can use it. All options are allowed except Backup and Restore due the Encrypted data.
Also Media Go works Ok.
I hope it works for you.
