Good idea, but it is not as easy as it looks at first sight...
First, on a purely hardware point of view, you will have to be careful, the GPIOs o nthe TL-WR703N are 2.7V only, NOT 5V nor even 3.3V tolerant.
You will have to adjust the IR receiver's output level to this voltage, the simplest is by using a resistor bridge. On the output side, you will have to make sure that a 2.7V drive level will fully turn on the IR LEDs too.
Basically, you will need 2 GPIO outputs and 1 GPIO input with interrupts. If you dan't want to mess with fine SMD soldering ,the easiest on the TL-WR703N would be to use the unmounted through-hole LED in parallele to the normal LED as the IR LED output GPIO, to wire the IR receiver in parallel on the RESET switch and to use the USB power (GPIO8) for powering the IR receiver.
Second, the kernel space driver: the proposed patch is using interrupts for the IR Receiver input, but AFAIK this is not implemented for the AR9331 SoC, only GPIO polling is working, so you will have to take the AR9331 datasheet and implement GPIO IRQs into the kernel first, or modify the driver to work with polled GPIOs, if it s possible.
Third, how to compile the stuff for AA: as explained above, this depends if you are using IRQs or polled GPIOs for the IR receiver's output: in the first case, this would require modifying the GPIOs handling in the AA kernel to support AR9331 GPIO IRQs and create a kmod-lirc-gpio kernel module for it. In the second case, only the additional kernel module is required.
In both cases, you will have to create a custom kernel package, check the Wiki:
http://wiki.openwrt.org/doc/howto/build
http://wiki.openwrt.org/doc/devel/start
http://wiki.openwrt.org/doc/howto/obtain.firmware.sdk
http://wiki.openwrt.org/doc/devel/packages