Firstly, mapping consonants to digits is hardly original, Derren Brown teaches the method in one of his books, and its one of the techniques used by people who do this seriously. Its also not very space efficient because all of your vowels are counted as whitespace.

Secondly, it would be a lot harder to randomly access the nth digit using your conventional method because you would also need to be counting the consonants as you go along through the sequence, rather than just +5 for every word.