Hi,
Sure, all you need to do is populate the lookup field that represents your relationship to the parent entity in your 'create' step in your dialog with the primary field of the primary entity in the form assistant (control on the left hand side when
editing the properties of your create step). In my screenshot, this would be the values to link the account (parent) to a child record that has a lookup to the account.

Rob
MCTS. GAP Consulting Ltd. Microsoft Community Contributor Award 2011 & 2013