Cannot open qt-creator two times on the same project

Since qtcreator does not allow me to debug two binaries at the same time (at least not easily) I tried to start a second qt-creator instance with the project open. But that fails with the error:

:-1: error: Cannot lock build graph file '/home/ablu/mana/build-manaserv-Desktop-Debug/qtc_Desktop_989aa9-debug/qtc_Desktop_989aa9-debug.bg': Already locked by 'qtcreator' (PID 3177).

Does this really need to be during the whole run time of the qtcreator process? If so it would be maybe cool if there would be an easy way to build to a different directory if the other one is locked...