Their membership organization, their rules and per their rules this is the only way to join if ancestor took that oath prior to April 9th 1865..."Ifproof of further Confederate service is available, thereby nullifying the Oath of Allegiance, the ancestor shall be considered for approval." http://www.hqudc.org/membership/http://www.hqudc.org/membership/
Why circumvent an organization's rules of membership that basically doing so would be a lie for you and the memory of your ancestor? Your ancestor made a decision and part of learning your family history is to accept what they did in the context of the times. Is it more important to you to join this organization instead of honoring the important decision and oath your ancestor made?