Tyler Graham is a pure-speed outfielder who can hit for high average.
In 100 games at AAA Fresno this year, he has batted an unbelievable .349 with 33 stolen bases in 100 games. He's not currently on the 40 man roster, but should receive a call-up for his impressive play.
As of now, the Giants' best pinch runner is probably Nate Schierholtz. Tyler Graham would add much depth to a Giants' team that is almost entirely devoid of speed.
Although they are packed with outfielders currently (Schierholtz, Rowand, Burrell, Guillen, Ross, Torres), they should be able to find an extra spot for him on the roster.