It can be done, off the top of my head, it would be something like this
create a new device template, with your manufacturer and name of your A/C unit.
tell it that it is an infra-red device, and that it belongs to category Climate Device, this will give it the thermostat commands group.
Once this is done, it will ask some questions about A/V devices, which will not be relevant, just ignore them and go through....
Then create a new IR command group.
But you should see the commands to be implemented (set fan, increase temperature, decrease temperature, on, off, etc..) and for each, you can make sure that your USB UIRT or GC100 is selected as the IR device, and learn each IR code, just like an A/V device.)
This is very new territory, because there isn't a device like this in the database already, but looking at the code, I see that it should be able to be done.