If the software supports getting updates, get the cracked copies to phone home and have a legal firm send them a warning they might be using hacked software.
Home users won't care, but legitimate businesses might convert to actual sales.
How would you send them a warning, you'd know nothing other than an IP address? If you just send the ISP a regular ol' "copyright" notice, there's a lot of ISPs who do not forward those notices.
And if you made cracked copies phone home, that's something that would get removed by the cracker anyway most of the time.
In my country, there is a branch of police that deals with such things. They have a relationship with an organization called Business Software Alliance, which I believe is formed with this specific goal- to allow foreign companies or their local distributors reach pirate users. However, I'm only aware of the major software companies being members of this org: Microsoft, Adobe, Dassault (Solidworks), Siemens.
"and have a legal firm send them a warning they might be using hacked software."
Rather send a message directly through the software and give a link directly to purchase it. A bit cheaper and more straightforward, than finding out adresses and involve lawers. That should be the last resort.
If the business is from someone in a low income country, they likely wouldn't care about any legal warnings either. Some of the software prices in those countries are very expensive relative to prices of other things.
If the software supports getting updates, get the cracked copies to phone home and have a legal firm send them a warning they might be using hacked software.
Home users won't care, but legitimate businesses might convert to actual sales.