Ideally you'd use a waveform monitor and an 11-step chip chart, but assuming you don't, does your camera have zebras for the viewfinder and can you set them to appear at different IRE levels?
70 IRE is close to caucasion skintone brightness and is one-stop brighter (Zone 6) basically than an 18% grey card (Zone 5). Some grey scales have stripes in different shades of gray, one corresponding to 18 % grey. You could set the zebras to appear at 100 IRE (on the white stripe) and 70 IRE (on the light grey stripe next to the 18% grey stripe.)
Then make sure your camera is locked off on the gain, at 0 db. Set your light meter to the same shutter speed as the video camera and then adjust your ASA rating until it gives you the same f-stop as what the camera is using to get those zebras to appear at the right spots (make sure you aren't shooting outdoors where you might need some ND filters, unless you know exactly the stop loss of the filter and can calculate that.)
