There needs to be an electrode attached directly to the silver in the image otherwise nothing will plate onto it - the plating requires transfer of electrons. It must be on the back of the print because the silver (on the front of the print) must be exposed to the electrolyte bath. Obviously the other electrode will be suspended in the electrolyte, probably a few mm away from the face of the print.
If the paper+emulsion are conductive themselves (means they don't need to be soaked in electrolyte, so you get your savings), I think you'll get problems with the Pt plating directly and uniformly onto the emulsion, regardless of where the silver image is. If the paper is soaked in electrolyte, there are no savings and I think you'll get plating onto the electrode on the back of the paper and not onto the silver image at all. In summary, I don't think the electroplating is going to work.
I think the chemical processes of either directly developing Pt/Pd salts or chemically replacing Ag with a more noble metal (i.e. toning) are used for a reason - they are what works. If you just want to avoid loss of expensive salt solution into FB paper, don't use FB paper; do your printing onto an impermeable surface like mylar film or glass.