You can put a passive crossover on the speakers. You would want a high pass filter to block out the lower frequencies that you do not want.
Here is a calculator that will help you with the values of the components that you would have to add: http://www.the12volt.com/caraudio/crosscalc.asp
You will also need to know the impedance of the speakers in your door that you want to block the bass from.
A first order passive filter will allow bass to come through below your selected frequency, but at a lower level. Higher order passive filters will block bass at the same frequency, but allow less bass below the selected frequency.