Had to jump through a few hoops to get this working, for those that are still having trouble doing so this is how I did it.
1) Go to misters (Define joystick buttons) and set up player 1 stick/buttons as normal, then add the extra mouse moves right,left,down,up mapping to any of the buttons on the player 2 side of your control panel but take note of your button mapping as you'll need this in the next step. Don't forget any buttons mappings you don't need skip with the space bar, but make sure to skip to the end or you mappings won't be saved (don't press escape key to get out of the mappings screen)
2)Load the Robotron core and select the fire option to (Fire: Second Joystick)
3)Move to the (Define robotron buttons) page and set up stick 1 as normal but when you come to stick 2 fire setup mappings press the player 2 buttons you mapped as mouse move right,left,down,up.
4)Now select (Button/key remap for game) menu and press the player 2 button you mapped for mouse move right and then move player 2 stick right, press mouse move left button on player 2 side and move player 2 stick left. Do the same for the down/up buttons and press enter on your keyboard to exit the remap setup. That should be it, you should now have twin stick action on your control panel.
Don't forget to (save settings) when you've got it working as it should.