Those diesel propane injectors just introduce the 'pane into the intake track, you should be able to inject the extra 'pane need with the nitrous the same way. As far as nitrous blowing out the propane, I don't think that would happen, otherwise nitrous would blow out the fuel in normal gas applications cause the fuel is sprayed in around 14 psi. Another way is to run a small gas tank just for the nitrous system, and use a fogger nozzle tapped into the manifold.
