I'm thinking two IR LEDs back-to-back (i.e. parallel, but reversed) across the right and left channels, with a current-limiting resistor, would suffice. Output a 19kHz tone, and you'll get 38kHz light (each lights on opposite half-cycles), so it would be just a matter of composing a .wav file, setting up the sound, and playing it.

I did a little testing here:

• Using an ALSA mixer from Debian, I'm able to get up to 2V p-p per channel; driving the channels out of phase gives 4V p-p, which should be plenty.
• With no ALSA mixer, just kicking the volume to max, I can get 2.5V p-p (both channels).
• Attenuation with both channels into a 110 Ohm load is about 20% (2V p-p), so it looks like the Thevenin impedance is about 25 Ohms for this configuration.

Allowing 1.3V across the diode, 1.2V into 25 Ohms gives about 50 mA, so no resistor should be needed. (Something like 100 mA if you do kick it up to 4V, but @~25% duty cycle, still no resistor needed if the LEDs are rated for at least 50 mA continuous.)

So just two IR LEDs and an 1/8" jack should do it, I think.