Quoted from MikeO:
Be careful if you bridge the gap with solder and then try to sand or dremel it. The trace material is relatively soft and any solder you apply will be relatively hard. When sanding, while your intentions may be good, it would be very easy to sand away the trace with any errant alignment of sandpaper before you get the solder sanded down.
I'd think long and hard before I proceeded with this approach.
Wet/dry fine grit will not sand off a copper trace unless you hand sand it for hours... I've used it for over 10 years. Solder always sands away a LOT quicker than copper from my experience. You only have to scuff it so the solder will stick, not go over and over it a ton. I would not suggest using a dremel for this unless you have a LOT of experience using one. You should get good results and not damage anything using hand sanding. Bridging the gap on the back side with kynar wire may work, but could get messy...
If you are simply going to try and move the fingers any way, you would't even have to sand after you bridge the gaps with solder.
One other thing I thought about is you could possibly use copper foil to repair the copper traces if they are really thin. The added thickness would probably be ok. You could test one of the pads by temporarily taping or glueing (or soldering?) down a square of copper foil to see if the added thickness will be ok.
I just noticed that this reiterates mhkohne's suggestion above.