Watch out for hot light sources. Unless your regular shooting is under similar hot lights, or if you know your light meter very well, I recommend to use sunlight or fluorescent light sources.(posted 8279 days ago)This is because hot light has higher spectral intensity in longer wavelengths, and most photodiodes and photoresistors are most sensitive to infrared region if no compensation filter is placed. The overall response pattern varies with each meter design. With many light meters, it is very easy to underexpose (or overread) with hot light sources.
With 120 format, no part of the film should be exposed to the ambient light when loading/unloading the film, so I see little reason to avoid using the leader/trailer as the base+fog reference.
My scanner has a lamp house for transparent material, and can load and scan 9 6x6cm frames or 24 35mm frames at a time, and my scanner driver allows me to void automatic adjustments. With some reference density steps, I suppose I can use it as a densitometer and make decent measurement fairly quickly. (I haven't started doing it yet.)