Disable data leads of USB cable
Much as I like hacking things, I think the simple answer here is a dedicated charger with a USB port.
my first attempt at solving your problem would be to get some kapton (or other non-conductive) tape and just stick it on top of the traces in your USB plug.
how about covering the two middle pins on the type A side of the cable with electrical tape? simple, reversible, and if you get it wrong, its a matter of removing the tape ;p