Hi, I've been searching this function a long time, so as I find it now, I share this tip.
Actually when you plug the tablet to your computer you have only one option : is Mass storage.
I prefer MTP (on Windows 7) because, the sd card is still available for yours applications on your tablet.
On my phone, I have a option in status bar when I connect it to my computer. Here nothing.
The option is somewhere else.
After opening the right settings bar, Click on Settings to open the setting page
Then select Storage.
Then click on the option buttons (on the upper right : the icon with 3 points)
A menu appears : USB computer connection, click it.
And we got it !
You can now select your prefered method for transferring files.
Then, the link in the notification bar will direct you to that page.
That's it !