Use the following cheat codes while at the Mos Eisley cantina and you will unlock the character you wish for purchase in Free Play mode:
Bespin Guard: VHY832
TIE Fighter: HDY739
Greedo: NAH118
Han Solo with hood: YWM840
Imperial Guard: MMM111
Gonk Droid: NFX582
Grand Moff Tarkin: SMG219
Jawa: JAW499
Bib Fortuna: WTY721
Boba Fett: HLP221
Death Star Trooper: BNC332
Ewok: TTT289
Gamorean Guard: YZF999
Beach Trooper: UCK868
Ben Kenobi's ghost: BEN917
Lobot: UUB319
Palace Guard: SGE549
Rebel Pilot: CYG336
Rebel Trooper from Hoth: EKU849
Imperial Officer: BBV889
Skiff Guard: GBU888
Sandtrooper: YDV451
Snowtrooper: NYU989
Stromtrooper: PTR345
The Emperor: HHY382
Imperial Shuttle Pilot: VAP664
Imperial Spy: CVT125
TIE Fighter Pilot: NNZ316
TIE Interceptor: QYA828
Tusken Raider: PEJ821
Ugnaught: UGN694