Sometimes it's amazing how people on opposite sides of the world get to working on the same thing. Paolo has been workin on using a simple MP3 player to play back the WSPR tones. He basically is trying to measure and control the time difference in playback so that he gets a cycle time which is exactly two minutes.
Check out his posting:
Addendum: Back in August, 2008, I experimented with using iTunes to send WSPR tones. I was concerned with the long term stabiity of sync, and in the end wrote a program which synchronizes itself with the system clock to send out messages. Had I been clever, I might have thought of taking Paolo's approach.
I also experimented with using this scheme to send QRSS3. It worked, but uncovered the stability issue that my FT-817 has when it is sending essentially 100% duty cycle.