If you have a customer that mines 24/7, 100% load, you'll make about $0.51 A YEAR at current diff, block reward and price....
But what if his software has thousands of customers? You can still make small profit and hold it till "better" times. But the software has to be auto adjustable, imagine working on pc with 100% CPU load Think about Antivirus blocking also, they can track and block this type of software. But anyway, yeah, diff will increase eventually
Donations or selling the software is not an option in your case?
If he had that many users anyway then monetization via ads would probably be a more profitable venture. Like others have said, mining with other people's low-end CPUs will not make you rich and it may be better to focus your efforts elsewhere.
Social media advertising seems like a new and hip way of earning money these days.