take your vocal sample and reverse it in your sound editor, insert enough silence at the end of the reveresed sample to take the revern tail, add reverb with a decay settign corresponding to your silence you put at the end of the sample 7-10 seconds is enough.
then simply reverse the sample again after applying your reverb and shift the new sample in your sequencer to correct timing....

also try adding another reverb after reversing the sample back again so it trails in and out ;)