Voted!
Hi Fab,
While this may be useful in some circumstances, my original post was in regard to Salesforce custom objects and the article states:
For use only with Marketo custom objects, not custom objects synced through the native Salesforce or Microsoft Dynamics integration
In that case then use Workato.com, we use it all the time for anything that falls outside of the abilities of Marketo and/or SFDC, including the scenario you are talking about