1. You need to work real hard at it well in advance multi-registering names multiple times at difference locations in same counties (maybe make use of middle names and initials to cut down on your frauduloent document production costs). Easier for the impersonators too ... less to remember.
2. You need to identify very low propensity voters and know how old they are, maybe some basic physical characteristics, personal stats like adress etc.
3. You set up lists with similar characteristics (guy/girl/ethnicity/age) and names of persons who can be spoofed or impersonated (depends if actual real name or not) on election day. You need the lists of similar design for polling day so you can bus your SWAT teams around to the polls quickly and have the same team spooof or impersonate maybe 20 persons on election day. Hell, with advanced voting over the dumb-assed length of times now allowed, the same guys/gals can spoof & impersonate hundreds of individuals ... maybe even thousands!
4. Take note with presidential politics you only need to stuff the ballot box in a few battleground states Florida, Virginia, North Carolina, Pennsylvania, Colorado, Ohio, Iowa, but the demonrats know that, and its not like the Republicans didn't know.
All of the above is eminently doable if you got money and brain-dead flunkie followers like the demonrats, andf an organization (Occupy Wall Street Hmmmmm ... who defaces their national flag with symbols of their candidate ... demonrats, that's who. Disgusting.
Republicans - If there's lot's of footage of persons entering polls in the batteground states, seems would be easy enough to look at footage from adjacent polls to see if familiar faces keep showing up to vote. Its not like there weren't lots of buses pulling up to the polls with gangs of people hopping off.
You've got the pollsters scratching their heads as to how the demonrats got the big numbers out. Now you know. Facial recognition S/W will make it more difficult to pull this trick next time round in 2016.
PS Now you also know why some were so adamant about not requiring government picture identification at the polls. Harder to conduct such an elaborate fraud.
Unlikely you say .... I say as unlikely as a Columbian under-graduate nobody remembers ever seeing. As unlikely as a Harvard Law Review editor who's not published (or what he did publish is so offensive to the general electorate that it was buried deep never to be seen again). As unlikely as a President who can't produce an unaltered long form BC or any school records or foreign visa documentation, even for $5M to charity.