I share your problem because I once took another car down through France solo driving and it was a key issue that all my 'toys' were able to be charged 24/7. Of course I'd worked out the battery drain was very low and the battery would be re-charged by daily driving.
I was re-charging portable satnav, MP3 player, phone and a PIR interior cabin security alarm to a PMR portable handset which I used for stopovers at motels.
Here's what I did:
1. Most modern cars have their cigar sockets wired through a relay controlled by the Canbus and are only active when the ignition is switched on. Although it is possible to locating the relay and jumper it, I wouldn't interfere with the oem wiring. It only needs the kids to leave their dvd player on at the back and you have a flat battery next day.
2. Most cars make it quite difficult (fire/smoke penetration) to find a route from the engine bay to inside the cockpit.
I decided keeping toys charged was best located in the glove box where they could be locked and hidden from view (Satnavs, mp3 etc).
2. I bought a cigar socket and wired it directly to the battery through a 10-20 amp inline blade fuse and holder. The fuse holder MUST be connected as close to the battery as you can get it. If you can get one, some have a built in led that lights up the outer ring. That nicely tells you the socket is powered and the battery fuse is o.k. If you don't mind buying more plugs you can consider the DIN size cigar plug/sockets used for trucks/marine which are smaller.
3. In my non-EOS car I had enough space behind on the side of the glovebox to fit the socket flush. That is the neatest mod., but may need the glovebox removed (not hard, even on an EOS). If you just want to dangle the socket in the glovebox, along with a USB cable for MP3 memory stick, that would work but is not so neat.
4. Next you have to find a route for the wires (at least 16-18 gauge!) through the bulkhead to the battery. I've not looked closely in the EOS, but you can sometimes find a 'passthrough' grommet you can use. If you find something convenient, post it up because I want to repeat what I did for the EOS. In fact EVERY car I might own in the future!
The trunk is probably another good place to have a 24/7 power point, but getting a neat wire route from the battery to the trunk can be challenging (under the chassis or in a cill box section maybe?) and you need the wire gauge increased for the longer run if you ever want to pull high current.