He doesn't even need to do that.
Add these to the CSS:
.sidebar ul li {
padding-bottom: 20px !important;
}
.sidebar ul li ul li{
padding: 0px !important;
}
Adjust the 20px to whatever size you want. And eliminate the empty widgets you were using.
Also, when playing with CSS, I highly recommend using Firefox and the Web Developer Addon. It will let you change the CSS contents of any page on the fly, and see what the results look like immediately. No need to change and reload over and over, just mess with it until you get it, and then copy and paste your results. Much simpler.