The GPS Emulator v1.2.0 that's part of Remzibi's OSD Configuration software now supports uBlox emulation. It has the option to enable NAV-VELNED, NAV-POSLLH and NAV-STATUS (which are the 3 messages ArduPilot uses for positioning).
ConfigTool.zip <- Includes GPS Emulator v1.2.4
EDIT: Here are all the sentences the emulator currently supports
NMEA
$GPRMC - Recommended Minimum Specific GPS/TR…