There is another way working for EVERYBODY.
Make a backup of your offline savegame. Then delete the folder. Make a new account with the exact name and online play. Just let it save and quit the game. Go to your savegame folder as shown in the other tip. Just rename the new savegame(playersave to playersave_bak) and copy the old offline savegame(playersave) in the folder.
Now open BOTH files with a hexeditor. Overwrite the first six lines (0x00000-0x00050) of the old offline(playersave) file with the first six lines from the new online(playersave_bak) file.
SAVE and start the game with the old offline savegame thats now a new online savegame with all your cars. Have Fun.
Just another tip: Somewhere in the first six lines, the money infomation(how much money your account has) is stored. But thats your task to find out where. There is a little protection when you start with a manipulated savegame. So just manipulate your money value one time. Buy everything you want and then roll back to your old money value with the hex editor. Yes it is a CHEAT. I hope eden games will change this until the release.
Have Fun and sorry for bad english.
If you do not know what to do. Just let it explain to you by somebody else. But not me.
Greezz djbban