Thanks, but that's kind of beside the point...
I shouldn't have to override the Excel export and code a whole bunch of stuff outside the grid, it defeats the purpose of having the Excel export there.
The whole point of the parameter map is to do just this, and it doesn't work when the Excel export binds the data source.
After all, the whole reason I have to do this is because date time pickers in filters are broken (per my first message).