In episode 6.05 The Lighthouse, Jacob wanted Hurley to push the Lighthouse dial to 108 (the sum of all the numbers). On the dial, we saw that each of our candidates and potential candidates were assigned a degree. Turning to that degree, would reveal a view into their off-island lives through the lookingglass.
And who was assigned 108? Some person with the last name of "Wallace". I believe this is too significant a name to leave to just anyone. Who is this Wallace? People have speculated that it might be Widmore or maybe Walt, but my (albeit random) theory is that Wallace is Jacob. Jacob Wallace.
Remember, Jacob said Hurley and Jack would get to meet him up at the lighthouse. What if turning the dial to 108 was the way into the world of Jacob. If Jack hadn't been so impatient and gave Hurley a chance to turn to 108, we might have gotten a glimpse into Jacob's off-island life, his backstory, or even an actual encounter.
Jacob being candidate 108 makes a lot of sense too. This supports the earlier mentioned Horcrux theory -- that he is somehow the sum of all the candidates.