Thanks for the clarifications. There is history of infusing an already-produced rum or whiskey using cocoa. This is one of the things Cacao Prieto intended on doing and they purchased a huge macerating tanks exclusively for this purpose. They were planning to distill the resultant liquid, but my guess is that a simple filtration process prior to bottling is all that is necessary unless you suspect microbial contamination from the cocoa.
My experience is that it's more efficient to use nib (over whole beans with shell) because of the increased surface area available. Nib will absorb the alcohol much, much, faster than a whole bean can - and that's reason enough to go with nib. Another reason is that it's going to be easier to remove excess liquid from a mass of nib than it will be from a mass of whole cocoa bean and shell. (You do need to find something to do with the paste from the nib.)
If you want to try something in the kitchen, get an ISI cream whipper and NO2 cartridges. Warm the container with hot water and then empty - no need to dry. Measure in some alcohol (sweeter - relatively speaking - rums and bourbons give better results than less-sweet spirits such as vodkas and many whiskies in my experience; gins are mostly a no-go), and measure in some refreshed nib (warmed up in an oven). Pressurize the container and shake. Wait 3-5 minutes before carefully releasing the pressure. You will have cocoa-flavored spirits -- and you can control the level of cocoa flavor by experimenting with the ratio of nib/alcohol, type of alcohol, other ingredients, and time spent macerating under pressure.
clay - http://www.thechocolatelife.com/clay/