[TYPO3-mvc] where do I set "CONFIGURATION_CREATION_ALLOWED" to TRUE?

[Tim Schoch | GSTALTIG]

Next episode:
After debugging the whole thing, I found that the needed configration is passed to propertyMapper::doMapping() as an argument. 
In this initial configuration Array «CONFIGURATION_CREATION_ALLOWED» is set to true for 
«Tx_Extbase_Property_TypeConverter_PersistentObjectConverter».

Then on line 171 the call to $subConfiguration = $configuration->getConfigurationFor($targetPropertyName); 
tries to acces $configuration['subConfigurationForProperty']['datas'] but that is empty (the whole subConfig is empty in fact).

Because the above flag is not set anymore, when attempting to map the array to the object, the exception gets trown.

I tracked the $configuration array to find out how I could set the subConfigurationForProperty and as it looks to me, as if there is no
way to do this. Where am I missing the point?

Tim