Yes, we all understand that. However, the client does not -- the client requires that the images be delivered with an embedded "resolution" of 300 pixels per inch. It doesn't matter that this figure is meaningless -- only that the client requires it.
To the original poster, sorry but I don't know how to do this with PS Image Processor. In Camera Raw it can be changed in the output prefs box, but I don't know if that will fix your problem.
I do this all the time in Photo Mechanic, using the Save Photos As menu option, and set all the parameters in that dialog box. Works pretty well.