There are wire saw blades that will cut steel among other things, the trade name is remgrit.

http://tinyurl.com/2atz57

But the blades are more of a rod saw even though the wire is just a length of cable. The bonding process makes the wire not very flexible at all. It is designed to be held securely in a frame, i would think that bending it around a small radius would shorten the life of the tool.

Remgrit also makes a complete line of cutting tools with bonded carbide including saber saw blades, recip blades, and bandsaw blades. I would think that the recip blades would be of more use if you don't have a frame to hold the blade in. The handle could be easily fabricated or purchased, if i remember correctly, Gerber even makes a multitool with a remgrit blade in it.

OBG, the only reason they used shoe laces is they didn't have power tools. A reciprocating saw makes short work of cutting metal or plastic pipe down in a muddy hole, just make sure you turn off the water supply before you cut the pipe. And don't take anyone elses word that "yes, the water is off".