with an optocoupler in place of the diode it would not matter, would it? The two circuits would be isolated. You could even go for a Darlington pair optocoupler just for good measure. The new IR diode could run off 3.7 volts directly from the battery instead of being limited to 1.8V or the component limited current on the other side of the opto. It's also just three components (or two if you buy an LED with a built in resistor); an optocoupler, an LED and a resistor. I'm not brave enough to give it a shot (I only have one n900). It is just an idea for anybody wanting a more powerful IR diode built into their N900. The optocoupler/LED/Resistor combo is in a sense a repeater and can be made very small ( easy to fit into mugen type cover).

P.S. would an IR Emitting Diode be called an IED instead of an LED? Not the explosive type obviously.