You might be able to do this with a wireless router/hub attached to a 10/100/1000 NIC that supports WOL on the target pc system. Both the bios and NIC must support WOL for any of this to work. Simply have the router stay on so it can receive the ethernet traffic containing the WOL packet which should be relayed towards the pc with the WOL compatible NIC. Yes that method will drain power from your battery slowly... it's the only wireless solution I can think of right now.
My speedstream 2623 uses about 12 watts @ 5v 2.4amps.
Netgear mr814 uses about 9.6 watts @ 12v 800ma
Maybe a wlan/ethernet bridge could also do this? Some more thoughts anyone else?