[swalberg]

Using the 26 letters from the NATO alphabet might be easier, it's made to be intelligible for non-English speakers over a radio connection with static.

http://en.wikipedia.org/wiki/NATO_phonetic_alphabet

[mustardhamsters]

Good starting point, but that won't get him trillions of combinations.

[jerf]

It does with 9 letters. In this case though I think I'd use them like a counter, so I would probably still top out at around 4 or 5.