I do not see an easy way to do that.
You would have to create a platform.txt with for upload that... uploaded the file onto the PC (via FTP or network share), then somehow kicked off avrdude on the PC (via some mechanism that you'd have to create).
Why can't you plug the arduino board into the mac? You can use an inexpensive USB hub to get more ports - all the macs in recent times have had USB...