Do let us know how you get on.
I've never tried this, but one issue I'd been concerned with has been how to do the control switching fast enough; using PWMOUT to switch the signal on and off might not give the timing accuracy needed as a result of PICAXE instruction timing.
Using PULSOUT to a control pin would allow an external 555-style modulator to be used and make it easier to generate correct pulse lengths ( and a PULSOUT to a dummy, unconnected pin allows the gap timing to be done ). To use this technique with PWMOUT would require some external logic, however, you may be able to get away with using just a few signal diodes ...
http://homepage.ntlworld.com/the.happy.hippy/picaxe/irmod.txt
The logic is inverted; keep CONTROL high to disable the signal, low to enable it. When either PWMOUT or CONTROL is high, there will be no positive voltage drop across the IR LED so it will be off, but when both are low the IR LED should 'light up'.