Breakfast Stout Clone - Secondary Chocolate Addition

6.6 lbs. (3.0 kg) Briess light, unhopped, malt extract
1.7 lbs. (0.77 kg) light dry extract
22 oz. (0.62 kg) flaked oats
1.0 lb. (0.45 kg) chocolate malt (350 °L)
12 oz. (0.34 kg) roast barley malt (450 °L)
9.0 oz. (0.25 kg) debittered, black malt (530 °L)
7.0 oz. (0.19 kg) crystal malt (120 °L)
2.0 oz. (57 g) ground French Pressed Sumatran coffee
2.0 oz. (57 g) ground Cold Pressed Kona coffee
2.5 oz. (71 g) Scharffen Berger Baker's Dark Bittersweet Chocolate
1.5 oz. (43 g) Scharffen Berger Unsweetended Baker's Chocolate
14.3 AAU Nugget pellet hops (60 min.) (1.1 oz./ 31 g of 13% alpha acid)
2.5 AAU Willamette pellet hops (30 min.) (0.5 oz./ 14 g of 5 % alpha acid)
2.5 AAU Willamette pellet hops (0 min.) (0.5 oz./ 14 g of 5 % alpha acid)
Wyeast 1056 Amercan Ale Yeast

I melted the chocolate (which came in bar form) in a double boiler and added it to the last 10mins of the boil. It mixed right in perfectly. After flameout French Pressed Sumatra coffee added when wort got down to 190degrees.

My OG was 1.063 at 65degrees and after 11 days its down to 1.017 at 67degrees.
The coffee taste is nice, smooth and fresh. Not bitter at all, the french press is definitely the way to go. The chocolate flavor is nice and subtle, but I feel like the original Founder's version has a more upfront chocolate flavor.
I'm already loving the taste of this beer, but I feel like when I add the Kona coffee to the secondary in a few days that it may completely mask the chocolate flavor. So I was thinking of adding some more chocolate in the secondary. But, I'm not sure what I should use.

Should I go with unsweetened nibs and soak them in vodka for a few hours to sanitize?

You forgot to use the chocolate nibs. This is an important part and you should be able to add them into the secondary. I brewed the same recipe but left out the Sumatran coffee as I added the crushed beans right into the primary which worked really well and had a good presence of coffee, almost too much at first. After a month in the keg everything balanced out and after 2 months that batch is perfect. I found its good to pour this beer with a good amount of head as the chocolate notes are best found there.

I've never had this original beer before but I can't think of any breakfast without milk! Add one to 1 1/2 pounds of lactose powder to the end of the boil, increase the serving pressure a little, and this will greatly enhance mouth feel and head growth and retention.

I didn't forget the chocolate nibs, I substituted them for Unsweetened Baker's chocolate that I melted. I talked to other people who did this and had good results.
I do have now though roasted cocoa nibs that I want to add with the Kona coffee into the secondary.
I'm just wondering what is the best method of sanitizing the nibs. Would soaking in vodka over night do the trick?

Trouble is you might extract flavors that way and would need to add the vodka as well. This might not be bad as I know a guy who used chocolate flavored vodka in the secondary to add the flavor to his brew. By this point your beer should have no oxygen and enough alcohol to fend off any minor bugs that might be in your additions so adding right to the secondary should not be a problem. If anything run a little Star San over the nibs and grounds.