Best Solution I can think to come up with is /castsequence reset=6 life bloom,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Life bloom,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Life Bloom,,,,,,,,,,,,,,,,,,,,,,, and just experiment with the commas to get the timing right.

Edit: Alternatively, you could do /castrandom Life Bloom,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,, to get it to go off once for about every 50 key strokes (or however many commas I put there). It really depends on how much you spam the button.

You could also do /castrandom Life Bloom, Rejuvenation, Regrowth,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,,,,,,,,,