Advice on location shoot

[another view]

I have a wedding coming up in April, and met with the couple today. The reception is at a hotel, and we can do some of the shots in the hotel's restaurant in the afternoon since it will be closed. It's a really great place to shoot but I need advice on how to light it.

This shot (available light) was about 1/30 @ f4, ISO800. The red arrow points at a walkway across the water that's about 3' wide (water is about 8' wide or so) and there's a waterfall about 6' behind the walkway. I'll put the subjects here and use the waterfall as my background. One camera position will be close to here or maybe centered, maybe 30' away from subjects. What I'm thinking about doing is putting a light on the left side maybe 10-15' from subjects. That way the window light will work as a fill.

I want to get something that's battery powered but don't think my Nikon SB28 is powerful enough to do it (with an umbrella?). I'm thinking about something like a Quantum Q4 with Pocket Wizards. I could probably find an outlet here to plug in a regular monolight, but that won't always be the case. I work alone so it has to be simple to use and carry.

Any help appreciated!