I spent a stupid long amount of time trying to figure this out for a mod I'm developing.
The only reason I post now is because I found an answer by simply searching for "load external library" and I hope no one will ever have to waste half an hour searching for this like I have.
All that is required is to place the jdbc connector jar in the mods folder, and forge will load it as an external library, allowing your code to utilize it.
EDIT: Oh yeah, that previous answer doesn't work because ILibrarySet is deprecated last I checked.