First, Lifepixel.com has a good, but not fully correct, pic tutorial on how to get in to the sensor.
A few pics showing how I deal with the process of getting the flat cables back in place. Although they are flexible they are kind of brittle too so best avoid too much bending.
The glass acting as the dust window/shaker is very thin and likely to break when removed (it did to me). To avoid to many fragments flying around, put a piece of clear tape over it before commencing the knife procedure. When the glass is off, do remove the small flat cable as well.
A tip on cleaning the new filter; Use dishwashing detergent with luke warm water and clean it well. I had some residue from the Scotch tape I covered the glass with while cutting and usually Eclipse fluid suffices in the removal of any remnant glue. But I had some streaks of the stuff that 5-10 tries with Eclipse failed at so out with the filter, down to the kitchen and voila, clean!
On a general note I can say that the G3 is very easy to modify (say compared to a D3xxx/5xxx series).
