That's true but I think the original question was how to get all three strains into one plant. The only way to do that is like what was posted earlier, hit a female with one type of pollen, collect up the seeds, grow them out, hit this F1 with another male, collect the seeds, grow these F1s and hit it with the third pollen, now you will have all three genetics in a new batch of F1s.
This is an extremely simplified explanation. If you're serious read the breeding threads on RIU. you will have to spend a few grows just to find the genetics you want from the first crossing, then all that times 3.
Good luck though. It's a lofty goal but not unobtainable.