I like Paris and hate tight connections, so I'd do it.

Catch the Orlybus into Paris (7.50€, I think). It drops you off at Place Denfert-Rochereau in Montparnasse. Several hours later, take the RER B train (a bit under 10€) from any of several stops to CDG. (There's one on the left bank very close to Notre Dame.) Be sure the train you take goes to CDG; the line splits toward the end and some go off in another direction.