If you really want to simulate GPS, you can use the command-line program "gpsfake", which is part of gpsd. This isn't trivial. Or, if you want to "simulate" having a "current location" in Maemo Mapper, so that you can use things like routing to a location from your "current location," then you can tap-and-hold on a location on the screen and use the "Set as GPS Location" menu item, in the "Tap Point" sub-menu.