Can I use epoxy repair putty as a permanent fix for a screwed through water pipe?
I would not trust it, especially in a concealed area where a leak could go unnoticed for quite some time.
You may be able to repair this yourself, if you know how to solder.
Supplies

Tool to cut the pipe (Oscillating saw should work).
Solder
Flux
Torch (MAPP gas preferably).
Steel wool or sandpaper.
Heat shield (preferably non-asbestos)
Appropriately sized coupling without a stop.

Procedure

Use an oscillating saw (or any other means) to cut the pipe near where the damage occurred (preferably right where the damage occurred).
Use the steel wool/sandpaper to clean/mar the pipe on both sides of the cut.
Lift one side of the pipe, and slide the coupling all the way on.
Realign the pipes, and slide the coupling so that the cut in the pipe is near the middle of the coupling.
Solder the coupling in place (careful not to start a fire).

NOTES:

How well this repair holds up, is dependent on your soldering skills. If you can't solder well, you may want to get help.
You might consider installing metal protector plates over the pipes, to prevent further mishaps.