Synchronisation MF ALM <-> Jira: How to prevent source specific mapping

We have Defects in MF ALM that should be synchronized to Jira as Observations.

After the initial creation, all changes should be done in the Observation in Jira and updated back in MF ALM, so the synchronization has to be bi-directional.

However there are also other Observations in Jira (out of different sources) that should not be synchronized to MF ALM.

I can not prevent the creation of Defects using the datasource properties, because in other mappings (for other issue types in Jira) Defects in MF ALM should be created. 

So I would need a Sync Criteria on Observation to only synchronize the objects that have previously been created through the synchronization from MF ALM. Or something similiar.

Any ideas how this can be done?