Here are some audio cables that might come in very handy. Most of them will transform your audio level from your audio recorder to match your dslr input and there are others that do more fancy stuff.
Here’s one of the cables I found useful: The DSLR-550D-HOCF takes your magic lantern loaded EOS 550D usb video output and turns it to a normal (3.5mm female headphone jack) audio signal.
[UPDATE] I realized that this cable is actually just an adapter usb to 3.5mm, no electronics involved. Most of the other cables incorporate electronic modules to control audio levels.
You can buy these cables here.