If you were to install the program to the flash drive before registering it, then it would work as long as the drive letter of the flash drive remained consistent, and as long as you only used it on the computer you installed it on.
I'm not going to lie, there *are* ways of getting around this problem, however they are not up for discussion here due to forum rules (circumventing the copy protection violates the EULA and we do not allow or condone conversation about it), and because of that I'm going to have to lock this thread.