To add a new library in Codebender click on the codebender gear in the upper left corner of the page (if you are on the code page) or "Upload library" on the upper right if you are at the home page. The library must be zipped. If it is downloaded from NT7S Si5351 or Rotary it is already zipped for you. In that case, just drag them from your download folder onto the Codebender "Upload a personal library" pop up that occurs when you press the green button.
Codebender allows me to embed my sketch into my blog where you can have your way with it. If you have Codebender installed on your browser, you can compile and download to your Arduino from here. If you want just the LCD_VFO_Si5351_IF.ino file for the Arduino IDE click here.