John McGaw
I can imagine ways that I might do the job -- inject non-toxic UV sensitive dye into the line for a while and then go over the line's path in the dark with a powerful UV light for example. In theory something like this would work but I don't have the means.

On the other hand, there are companies which do this sort of work all the time. I don't know what they charge so it might be cheaper to just have somebody come in and bury a new PEX line (which is what I did last Autumn) but it couldn't hurt to ask around. Disclaimer: No connection etc.