Ya, I can say I'm one of those people who are against hybridization, especially to create a mutation in a particular species. I'd rather have a natural mutation than a hybridized one, because you never know what problems may arise when hybridizing two species. I also believe there may be a higher chance of health problems in hybrids rather than pure species, but then that would depend on how close the parent species are.
With that aside, the best way, IMO, to produce "mutation" alexandrians (going from a hybrid point of view) would be to either breed an alex to a dominant color IRN or have two hybrid pairs (recessive mutatin IRN x Alex --- x2). You'll get green offspring from both pairs who are split for the mutation, and then you can breed the resulting clutches from each pair together, and have a chance of producing visual colored offspring. If you ensure to breed various pure alex's into the hybrid offspring, you'll get chicks who look more and more like pures rather than hybrids, yet still have the possibility to throw mutations.
Breeding hybrids together to produce a mutation in another species isn't unheard of... as supposedly some lovebird mutations came about via hybridization (I believe it's in the black masked lovebirds, but could be wrong), and I've heard reports that the red factor sun conure is the result of hybridizing with jendays and then breeding red intense birds together.
Here's a good article on the subject!
Mutations In The Alexandrine Parrot <--- Breeder of Hybrid Alex Mutations
IRN Mutations <--- Also A Breeder of Hybrid Alex Mutations