In Lightroom, it’s easiest to do this in Library mode, but you can do one photo at a time also in develop mode.
Click the photo or photos you want to make a black and white version of and then select “Create Virtual Copy” from the “Photo” menu, or just hit Command + ‘(Mac) or Control + ‘ (PC). You’ll notice, if you selected several photos in library mode, all the new versions become selected. To save yourself some hassle, you may want to assign a color label to all of these by pressing 6-9 so that you can easily single out the black and white versions later if you need to.
Now, just apply the black and white preset you want through the “Saved Preset” menu in Library mode, or just in the Presets panel in Develop.
In ACR there aren’t virtual copies, so the best way to do this is to manually duplicate the photos you want to create black and white versions of either in the finder or in Bridge.
In Bridge, just select the photo or photos you want to add new versions of and select “Duplicate” from the Edit menu. (or you can right click and select Duplicate) This will physically duplicate all of these files, so beware of hard drive space implications. As in Lightroom, when you duplicate the files in Bridge, all the new versions will be selected and you can save yourself some hassle by pressing Command + 6-9 (Mac) or Control + 6-9 (PC) to assign a color label to them all so you can single them out later if need be.
Then as always, open up these new versions in Bridge and apply your favorite black and white film. To apply to multiple photos at once, just shift click all of them in ACR and apply the preset.