Since I have been into varanids, there have been lots of people saying "they" have a way. One day, one may.
The problem with a method is, it only takes a few failures to ruin a method.
The truth is, most individual monitors are easily sexed. The problem is, some are not. The other problem is, what exactly is a baby monitor? one day, one month, one year, two years. Some people think a two year old is still a baby. Back in the old sonogram and X-ray days, they said they could sex baby monitors, I asked how old and they said a year or two. Hmmmmmm By then, we are on another generation.
Today is not much different then the past, a little better, but not much. It really does not matter what sex any individual monitor is. The reason is, what sex they are is not the limiting factor in varanid reproduction. Poor husbandry is.
For us, we make no effort in sexing monitors and we always have both sexes. Hmmmmmmmmmm So I would rather dwell on other things then buying a book to sex monitors. Good on him. Cheers