First a bit of backgound ...
To get a nitro head on canned or bottled beer you need two things. Nitrogen dissolved in the beer, and some means of getting the nitrogen out of the beer as small bubbles.
The US version of the original Guinness draught flow patent specifies a dissolved nitrogen content of 0.015 to 0.035 vols. This may not sound like much but that equates to about 40ml of nitrogen in a pint, and is enough to create a 1cm head. Professor Charles Bamforth is the undisputed King of Froth. In this paper he explains why nitrogen produces a much better head than carbon dioxide. In short the difficulty in producing small bubbles is that surface tension means the gas pressure must be higher. In a typical beer the pressure inside a 1 micron bubble is about 3bar. With CO2 the gas at pressure dissolves into the wall of the bubble, and can then effuse into an adjacent bubble. By a process known as disproportionation small bubbles get smaller and large bubbles get larger. Because nitrogen is much less soluble in the bubble wall it has a far lesser tendency to disproportionation. Hence it will stay as small bubbles, and a thick dense foam.
So back to the dual problems of dissolving nitrogen and creating small bubbles. The problem with bottling nitro beer is that nitrogen won't stay in a supersaturated solution in the way that CO2 does. As soon as the head pressure is released from the beer the nitrogen comes out of solution and is gone. In order to counter-pressure bottle it the head pressure must be maintained while the bottle is capped i.e. the whole mechanism must be in a pressurised chamber. Left Hand have been pretty quiet about how they get round this problem, but another brewer, Vault, has hinted that they inject liquid nitrogen into the bottle and then cap it quickly before it all boils off.
It's not clear whether Vault do anything to assist the formation of small bubbles other than the "vigorous pour" advice. I've seen speculation that Left Hand etch the interior base of the bottle to provide nucleation sites. In the canned version of Nitro Stout they use a widget similar to Guinness draftflow system.
Whether you can do this at home depends on your access to liquid nitrogen and nano-tech. However, the easier way to get a nitro head is just to bubble nitrogen (or even air) through a 0.5 micron carb stone after you've poured the beer.