Why do you "Need" to move it to secondary? How long has it been in primary? Many beers can finish without ever going into secondary. Unless there is something else going on, you can probably wait long enough to find and prep the ingredients you really need.
I wouldn't use bakers coco (i assume that's what you have on hand) simply because of the amount of percipitate it can leave in the final product. I also dont think its as potent as nibs. Whole foods, groceries with organic/health isles (Nibs are a super food supposedly) or even amazon are good solutions for ingredients in absence/instead of LHBS.
Regardless of what you use, it should be sterilized before addition to secondary. Soaking in vodka works just fine. After a soak of 24 hours or so, feel free to pour the addition and the vodka into secondary so that you get any flavor leached out by the vodka.