Hi Dennis, thanks for your question. I know of no easy way to stimulate the deep posterior tibial nerve electrically. The sciatic nerve and its man branches in their most proximal course is about the deepest peripheral nerve in the human body. I attach two texts on surface nerve mapping, and one text on magnetic nerve stimulation. I do not know of commercially available magnetic nerve stimulators, but there could be. Teleflex sells the "Stimpod" with surface nerve mapping options, which is my recommendation. There are others on the market as well.
I have surface nerve mapped the sciatic nerve distal to the buttock in children, who are thin, but rarely is an adult thin enough to achieve this. Be cautioned the current needed for positive surface nerve mapping is very uncomfortable for most conscious people, other than a highly motivated individual like me and my volunteer trainees.
You can also try to use the Super Inductive System (electromagnetic field EMF) which depolarize the motoneuron without the need of contact electrodes or needles.
It allows therapy delivering without direct skin contact. The therapy is based on the interaction between the high intensity EMF and human body. Once the EMF is generated by a coil placed in the applicator, neuromuscular tissue is depolarized and muscle contraction occurs. Based on the selected stimulation frequency, muscle facilitation or strengthening can be achieved, effectively