If you don't mind keeping the camera lens cover open, I'm pretty much sure you can set the 'flash'/recording LEDs blink in some regular intervals just as the status LED does it on the front panel. Shouldn't chew the battery if the interval is sensible enough. Even if you keep the cover closed, white LEDs blinking will be pretty much visible in the dark.

This is probably the easiest and the most battery conserving method I can think of.