To be precise I have built yocto linux-image using bitbake tools and the default desktop was just matchbox_terminal, in this case the solution is as follows:
1) Turns out you can use a .Xsession file in your users directory, but be careful to use a big character X, some resources indicate that the file name is .xsession which wouldn't work in my case.
2) Prepare your .Xsession file appropriately - an example:
#!/bin/bash
/usr/bin/x-session-manager &
exec /path/to/your/Qt/app/binary
3) That's it. At this point the first thing which will show up is matchobox_terminal, if your application takes time to load then it might be an unwanted situation. To hide the terminal just backup your /usr/bin/x-session-manager file and comment out the line showing "matchbox-terminal&" in the original one. Now you should see just a black screen with mouse pointer before your application loads.
