G'day John,
after searching through the recesses of my mind (I don't like going there 'cos it's dark and scary) I seem to recall that you can indicate this by using an accidental in conjunction with the trill symbol... 'ang on a sec....
Ah HA!
Just checked my Alfred's...
You can use an accidental after the TR but before the wavy line (if used) OR the accidental can be placed above the trill symbol. You can also use a cue sized note head after the principal note with the accidental placed before it...