I got worried about this and I tried taking a gem clip (one of those big paper fasteners with the fold-out wings) and securing the end of the male usb connector with it (leaving it on for long period of time when it's not plugged in or connected to the phone, obviously). I was hoping this would exert a little force on the tiny clips on the plug. It seems to be working; the few times I have plugged in the phone since starting this process the connector has gone in or out more easily.

I also bought a spare battery and a charger for it, just in case. :-(