How to combine two cart line items under same promotion

If we have a multi-buy promotion, and qualifying count to be 3, so if we increase the quantity to 6 , then a separate line item is created by promotion engine, any suggestions , if possible, to combine these promotion line items into one and non-promotion line items as segregated.

Is there any possible situation to specify in promotion engine to set parameter.setCreateNewEntry(false) in promotion evaluation. Thanks