Adding custom links to the right hand side of the start menu would require a code guru.
Taken that I'm not a code guru and would still like a custom link on the right hand side of my start menu, there are a few work arounds to this.
The Documents, Pictures, Music, Video, Download links can be routed to whatever folder you want.(You can enable/disable these librarys from showing in your start menu by right clicking on the taskbar, going to the start menu tab, and selecting customize.) The downside of this is that you can't change the names of the libraries.
In my example, I have all my documents stored on a secondary internal HDD. (E:/)
Step 1: Start -> Right click on Documents -> Select PropertiesOption 2:
Step 2: Click "Include a folder"
Step 3: Browse to your given directory, and click "Include Folder"
(In my case it is "E:\My Documents")Step 4: In the Library locations box, select the directory you just chose, then click "Set save location"
Step 5(Optional): you can remove the default directories so only the directory you specified is opened when you go to the documents library
Step 6: Click Ok, and it prompts you if you want to move all the files from the old location(s) to your new directory. This is up to you, I say no.
Step 7: Hit Start -> Click Documents to verify it points to your new directory.
Very similar to option 1, but with a little more customization.
Step 1: Enable favorites menu in taskbar properties -> start menu -> customize
Step 2: Right click on favorites when in the start menu, and select properties.
Step 3: Under the location tab, change the directory to whatever you wish.
Step 4: Click ok.
This option is nice because it allows you to browse the directory as a menu.
I think of these as redneck workarounds, but take from it what you want