The new, fake cert just has to validate for your phish/drove-by/cred-jacking site that is mimicing a real site. You are not planning a long-term take-over but

The new, fake cert just has to validate for your phish/drove-by/cred-jacking site that is mimicing a real site. You are not planning a long-term take-over but just to make sure the new site passes checks by your victims.