The simple answer is that you cannot do this (easily) with ggplo2.
You can add secondary axes, but these must be one-for-one transformations:
I don't know enough about your data to understand whether these transformations are possible.
A more complicated answer is that you can produce any dual-axis plots but that means hacking into the grid system, which requires more advanced expertise.
The base plotting system may be more straightforward for you in this case.