You have three options, first, just pass the craeted BO over as a parameter to the child form. Second, manually add the item to the translation collection.
'-- Decalre this as a private on Form1
Private _MyBO As MySourceBO
'-- Manually add the translation
Dim loItem As New MicroFour.StrataFrame.UI.Windows.Forms.BusinessObjectTranslationItem()
loItem.SourceBusinessObject = "Form1._MyBO"
loItem.DestinationBusinessObject = "Form2._DestBO"
Me.ChildFormDialog1.BusinessObjectTranslations.Add(loItem)
Last option, manually translate the BOs yourself by calling the translater directly.
MicroFour.StrataFrame.UI.Windows.Forms.BusinessObjectTranslator.TranslateBusinessObjects(SourceBO,DestBO,"DestBOInstanceName",Form1,Form2)