I looked into the site and I can see that the way of implementation I suggested earlier can solve the problem.
But did you try "simple" members search? On member directory search there are 2 kind of searches - simple and advanced. Using simple search a visitor can just type the name he looks for and the system will show the record instantly (it would be narrowing the full member list during typing).
Give it a try - this might help you for now.
Evgeny Zaritovsky,
Apricot's Kernel
Wild Apricot team