You need some way to kick off an increased amount of urbanization, increased bureacratic effectiveness and a change in military strategy able to conquer and hold vast swaths of land and smack down any potential powerbase that can challenge the central state. This is difficult.
Perhaps it would be best to kick off Italy's urbanization much earlier whilst facilitiating technological and agricultural transfer from the Muslims much earlier- i.e, bring papermaking, rice, windmills and so forth to both cause a population boom, a period of vast economic growth and increased state organization that leads to a strong centralized state in Italy eager to expand. (and of course, declare independence from the HRE)
Italy might be your best bet since the North can be nicely fortified, the Po valley is very fertile, the crops can be diversified well IIRC and of course it had plenty of contact with the Muslim Works during this time period.