there is but im not sure exactly what it is since i've never used it.
check the mame.ini there are a bunch of video settings in there.
also you can do mame -showusage at the command line to spit out a bunch of configuration options.
this is probably what you want here..
"-numscreens number of screens to create; usually, you want just one"
but there are more video options as well.
-screen explicit name of all screens; 'auto' here will try to make a best guess
-aspect aspect ratio for all screens; 'auto' here will try to make a best guess
-resolution preferred resolution for all screens; format is <width>x<height>[@<refreshrate>] or 'auto'
-view preferred view for all screens
-screen0 explicit name of the first screen; 'auto' here will try tomake a best guess
-aspect0 aspect ratio of the first screen; 'auto' here will try to make a best guess
-resolution0 preferred resolution of the first screen; format is <width>x<height>[@<refreshrate>] or 'auto'
-view0 preferred view for the first screen
-screen1 explicit name of the second screen; 'auto' here will try to make a best guess
-aspect1 aspect ratio of the second screen; 'auto' here will try to make a best guess
-resolution1 preferred resolution of the second screen; format is <width>x<height>[@<refreshrate>] or 'auto'
-view1 preferred view for the second screen
-screen2 explicit name of the third screen; 'auto' here will try tomake a best guess
-aspect2 aspect ratio of the third screen; 'auto' here will try to make a best guess
-resolution2 preferred resolution of the third screen; format is <width>x<height>[@<refreshrate>] or 'auto'
-view2 preferred view for the third screen
-screen3 explicit name of the fourth screen; 'auto' here will try to make a best guess
-aspect3 aspect ratio of the fourth screen; 'auto' here will try to make a best guess
-resolution3 preferred resolution of the fourth screen; format is <width>x<height> [@<refreshrate>] or 'auto'
-view3 preferred view for the fourth screen