How do I encourage new roots on Vanda?

[kwarren]

I have had a Vanda Pachara's Delight for several years in my brightly lit south facing solarium. It has a large healthy batch of roots at its base and it gets dilute fertilizer every time I soak or spray the roots so it flowers 2-3 times a year. Over time I have lost the lower 9" of leaves as the top continues to grow. I've heard that once it gets too tall and a new healthy crop of roots have formed from the leaf axils that one can cut the top off to produce a shorter plant. The original mass of roots below the plant's base continues to grow and multiply but no new roots have grown from the leaf axils. Can someone please advise me how to encourage new roots from the leaf axils?