In MiddlePage2, add an event handler for the WizardNext event. In that handler, look at the combobox setting. Then, if it's set, change e.NextPage to "MiddlePage4", rather than "MiddlePage3".
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Skipping pages
In MiddlePage2, add an event handler for the WizardNext event. In that handler, look at the combobox setting. Then, if it's set, change e.NextPage to "MiddlePage4", rather than "MiddlePage3".