Supported camera formats only allow certain resolutions?

Hello everyone. I'm looking to write a GUI in matlab that will allow for previewing and recording of two videos at the same time from two cameras. At the moment, attempting to preview them both at once causes the frame rate of the second camera (whichever one is started second that attempt) to have the frame rate drop to unnacceptably low levels (0.1 FPS low). I was hoping that I might be able to downsample the resolution on the camera so that the native frame rate can be higher - using the software provided with the camera shows that by dropping from 2560x1920 down to 800*600 the frame rate can increase ten-fold, from 3 FPS max up to 36 FPS max. But although the software that came with the camera accepts many formats and resolutions for changing the input of the camera, matlab will only accept the 2560*1920 size, and will rewrite the existing camera parameters up to that size if necessary - killing the frame rate. Is there any way for me to add more formats to the ones shown by imaqhwinfo('winvideo') -> Supported Formats, to allow for downsampling?

Much appreciated.