Can you get a girl pregnant with the opposite hand you wiped the pre-ejaculate off with?

You always run the risk, but unless the pre-cum was introduced into the upper vagina or cervix, you'll probably be okay.

Pregnancy occurs when the seminal fluid of a male reaches the egg of an ovulating female. Those wishing to avoid pregnancy should take great precautions with any reproductive fluids.

One should assume all fluid coming from the male's reproductive organ can cause pregnancy.