So it isn't easy; should it be? If one wishes to exercize the right to have a say in their and their countrymen's future shouldn't it be worthy of a little more effort than buying a lottery ticket?
The point is, it isn't impossible or even particularly onerous as a onetime endeavor. If they move around a lot, they may not be voting correctly on precinct level local issues, but the overarching purpose of restricting one man to one vote is served and restricting a voter to only the local issues affecting the precinct in which they live is attempted. Perhaps an individual who doesn't want his real residence to appear in any database would be worthy of further scrutiny before being automatically accorded the rights and privileges of proper society
It should be as easy as it is for the government to take taxes out of your check. That's a fair trade isn't it?