There is nothing unique in the BIOS that can be relied upon from all boards you may encounter. The newer Intel CPUs have unique CPU IDs that would be ideal for that purpose, but it's unreasonable to limit yourself to customers with newer Intel CPUs.

One does wonder how you would achieve this anyway, short of running a program to harvest the info from the client and transfer that info back so that an install package could be branded before distribution.

In any case, limiting the product to a specific box would not be very customer friendly unless you had an easy to use mechanism to support customer hardware upgrades.

Have you considered the much hated dongle?