Okay I got it to work. The secret is to do your partial space switching gesture (for me it's a swipe with three fingers and then in the middle of the swipe without releasing your fingers, press command-space to open spotlight and type the name of the app you wish to launch, then release your fingers after the app has launched.

As the other user said before me, the app must not be open at that time and it must not be in full screen mode. The only disadvantage is that only the first app can be in "full screen mode" and the app that isn't in full screen mode does not show up properly in mission control or in the app switcher when you press command-tab. Interesting way to use that lost space while one app is in full screen mode, but it's a shame that it doesn't work as well as it could if Apple officially supported this.