It is possible to force the resolution using command line parameters, at least on Windows.
For example:
-screen-fullscreen 0 -screen-width 800 -screen-height 400
(That will run the simulator in a 800x400 window)
I think it is possible to use command line parameters on a Mac too, but I don't know how, I'm not a Mac user myself.
Perhaps you can find some information on how to do that here: https://superuser.com/questions/16750/how-can-i-run-an-application-with-command-line-arguments-in-mac-os