There's a single close up shot of Obi-wan climbing out of a pool of water before it transitions to a master composite shot. So it's possible that, if nothing else, that could've been a complete on-set shoot.
SilverWook said:
Being asked to play your emotional scene opposite a tennis ball on a stick is another matter. ;)
That and George Lucas altering the script on the day leaving you with maybe three minutes rehearsal time.
