You can use the Sonitus:fx Modulator for a Vibrato effect if you want to try that (courtesy of Craig Anderton)
Use Default Flanger Preset. Set rate to 6 hz. LFO to sine. Phase to 0. Delay to 0.01 ms. Mix to 100%.
The depth slider controls amount of effect.
This is straight out of Craig's X1 Advanced Workshop: the next level dvd. Lot's of good stuff
Steve