If you can't wire cat5 to your PS3, then your only other choices (besides wireless) are: PowerLine (200Mbit high speed version) and Ethernet over Coax. Both alternative solutions are expensive.
I've seen the reviews of the Netgear Ethernet over coax kit, and they look interesting (hxxp://www.smallnetbuilder.com/content/view/30743/51/
). Netgear makes a Ethernet over Coax kit, however I have not found any on sale.
I'm using the Linksys PowerLine PLK200 kit, and they work better than wireless, but not as good as cat5 Ethernet. I can get close to 85Mbit, with the two devices separated by one room. Of course PowerLine will not work across two different electrical circuits, so make sure your two locations are on the same circuit, before investing in PowerLine. Powerline performance will also vary widely depending on the quality of your electrical circuit, and distance between the two location.