I would think the only real way would be using 2 detector/cleansweeps side by side,bu of course the you start getting into problems of the setup being VLF based would in theory only work on dry sand,then of course the biggest problem is that you are looking at using a data logging device on the setup,which i dont think would work very well.
Interesting project and i can see what you are trying to achieve,but with the detector and coil and the data logger that you have suggested and also the beach conditions could well be very hard project.
I would have said that its achievable if you use a pulse with a frame based coil,i have a 36''x36'' frame coil that i have been experimenting with and it may be possible and make into the shape of a very wide coil say a very wide but narrow footprint,that would work i would think and also work on both wet and dry sand conditions unlike the Tesoro VLF set that you have mentioned,but then one problem is that we dont have a clue what/how data logger you had planned on using ??
I personally think it would be a waste of time going down the VLF route especially the tesoro option,but could well work or achievable with a Pulse setup.