I have a little bit different setup, so not sure if that makes much sense for you...but in any case, there it goes.
I have installed berryboot and from berryboot I installed both Raspbian and OpenElec (I wanted to try both).
So in order to have some content in the SD card to use it as a demo content to show to friends, I first established a shared folder between my raspberry and the pc (using samba for that, piece of cake
After that, I boot into Raspbian and copy the content from the pc into the home folder from the raspbian system. Once the content it is in Raspbian you can either watch it in raspbian or just exit.
Reboot the Raspberry and this time log into OpenElec.
When OpenElec starts, click on Videos->Files->Add Videos -> Browse -> RootFilesystem ->/media -> berryboot -> data -> Debian_Wheezy_Raspbian_2013.05.img192 -> home -> pi -> and here add the name of the folder where you have your content (or browse until you find it). This way you can add your content into Raspbian and then find it from OpenElec.
I am sure this is far from optimal and elegant solution, but it works. I was trying to make a separate partition for content, but didnt manage.. I will keep on trying though
Hope this helps you