I must be wrong at what you are looking to do, but I believe this is the work around. pin it to start menu. I am sure you actually want it on the right side. There should be a browse option to add folders of our choosing to that side built into the start menu customize window, but there's not.
Try this - create a new library with just that folder in it or place all your files in the new library directly - How to Create A New Library In Windows 7 » My Digital Life
when you create the library - you have to click properties to add folder to library. But when you're done i'm sure you can open the folder inside the library and drag all the file into the library itself - just label the library my documents like you wanted to in the first place.Just wont be in right pane, so you may as well just drag your my docs folder into the left start menu pane. this whole idea is a waste of time, can just paste the folder itself instead - i just did it- i thought the new library would show on right pane - no luck wtf
Short of renaming one of the libraries you do not use - i see no way of doing this.
Trying to help out - good luck