While I don't currently have a similar requirement... this should be doable using the "Only Before Sequence" option... the problem here is that the contain must have at least 2 conditions separated by a "then" (which might remove one addition page from your segment.
In theory you could create a segment at the visitor level, add a "visit" level container, and create a sequence:
When you use "then", a new icon will appear that allows you to dictate additional filtering, such as only before sequence..
in theory, this should pull back all data for visitors that completed a "create account" flow, but only contain the pages and hits that occurred before they went to create account page and created their account.