AFAIK N900's IR diode's (+) voltage is connected with battery - the problem is with element after (-) side of diode (can't remember name now), which got pretty low limit of current passing.

mini Ir repeater, wired inside N900 with bigger cover (aka mugen one), could make it possible to put everything inside device. Still, it would require pretty nifty miniaturization, and would rather require single battery (no dual-scud + ir repeater inside, sadly, unless you can prepare it from really micro components, and solder under microscope).

/Estel