Thanks for your replies Usagi and Bill.

Usagi, I too would be concerned about the repeatability of switching an enlarger on and off with the ramp up and down of the light intensity. Rather than waste another 5 rolls of film I would rather first do some test to convince myself of its repeatability.
My light meter measures flash output with and without a synch cable attached (I just have never tried it), and it is possible that such light meters can measure/integrate the light intensity over times longer than the micro seconds a typical flash burst lasts.

Having said that I am still trying to convince myself that the in-camera method can work for me (see my last post to Stephen)