Although you cant get the separate panels to display across multiple monitors you can 'cheat' a little.

Click on the window icon on the title bar so that it is no longer maximised, then drag whichever side of the window you need to stretch to another screen. You can then adjust the split area to roughly position it between the two monitors. This will give you two panels on each monitor. Be aware though that adjusting the height of the window on one monitor will also change the height on the other.

Clicking the maximise button on either will return the display to a single monitor again. Bear in mind that you will need to do this each time you load Blender.

Its not a perfect solution but does help now and again.