Actually, there are 2D Engines that support realtime scaling. But for WME a way would be to recreate the scenes for different resolutions if you think its necessary. So you could write a small tool that changes the game resolution, and then load the according scenes ( for example, scenes would be in folders called 1024x768/scenes/bla/bla.scene , so the structure would be the same for every resolution ).
Anway, if you choose 1280x800 as resolution, it will run perfect on most desktops/notebooks. On 4:3 screens you'll have black bars on top and bottom. Most 16:9 / 16:10 gpus / displays support 1280x800 nowadays.