What I've done is record my own WSPR tones through the sound card's digital loopback. The transmitted message is always very simple "M1AVV IO84 37", so one 2 minute recording is all that I need unless I change grid square from IO84 or use a different power level. I saved the recording as a 22KHz, 8 bit mono .wav file (didn't want to use an mp3 because the mpeg codec might affect the tones).
To play back the sound, I connected a very short cable between a 3.5mm jack plug and an RJ45 plug. One end goes in my Nokia E63's headphone socket and the other into the mic socket on the radio. With the radio in VOX mode, all I have to do is wait until the correct time (a multiple of 2 minutes) and press play. As long as the volume is set just high enough to give the full output power on the radio, it is OK.
I tried this with my Icom IC-7000 on 80 metres tonight and some stations received my signal so everything must have been working. I'm going to try it with my FT-817 another time out portable or even when mobile. If I add a few minutes silence after the tones and put it on repeat, I'll have the proper tx/rx cycle and could leave it going while driving around.
This still doesn't give me any receive capability but it's useful for a beacon. Another idea is to use the phone's alarm clock function to trigger the sound, so it can be automatically synchronised to the time.
Here are the results from my Nokia generated tones (a single 2 minute transmission):