Create SalesOrder from Quote filtering some rows

Hi

I'm using Microsoft Dynamics CRM 2011.......

When User call the Create Sales Order button from a Quote, then the CRM creates a new Sales Order with same details (rows).

I want to filter some of these rows using plugins and C# (PreSalesOrderCreate?). For example: I want to exclude the rows which have a custom flag (Yes/No option set) "exclude" set to true.

Is there any method to do this?

Thank you very much

Matteo