Membership for Matching Challenge

I am about to start a matching challenge campaign where our current donors are asked to increase their support a 1/2 step up from their current membership level. Our matching challenge corporation will match the increased portion of the gift to upgrade them to the next membership level. For example, a $500 member who renews their support with a gift of $750 will receive benefits of the $1,000 level compliments of our matching challenge corporation. 

Has anyone done this type of matching challenge before and if so, how did you track the membership? We won't be receiving funds from our corporate sponsor based on participation in the challenge so we can't book a pledge from the corporation and soft credit the individual. If we manually upgrade the memberships, any subsequent additional gifts throughout their membership will recalculate their membership level. We could create special membership levels, but I don't think that's ideal. Does anyone have suggestions or recommendations? Thanks!