The trouble with using transliteration from one language to another is it can encourage bad habits - the student can think 'this sound equals my sound' (or - worse - 'this phoneme = my phoneme'). If you're going to have to learn a new system, why not use the IPA (there's an interactive chart you can download here: BBC | British Council teaching English - Downloads )
[note: this download gives British English audio, though I'm sure it wouldn't take you long to find another one if that's not want you want.]
Of course, your student would have to learn it too. But the same British Council site provides loads of resources, and when they've learnt the system it'll make dictionaries infinitely more useful (so the student won't be 'locked in' to your home-made transcription scheme).