Maybe with some sort of detachable and reattaching panel and the bottom of the fuselage to allow easy separation of the warheads, possibly with some advanced systems to release them either all at once or one here and one there controlled by a local human-in-the-loop operator located at the front of the reusable part.
Make the wings/engines detachable and have them return to base, a la reusable boosters.
Also if you turn the main body into a MIRV carrier, the main fuselage should be reusable too.
Maybe with some sort of detachable and reattaching panel and the bottom of the fuselage to allow easy separation of the warheads, possibly with some advanced systems to release them either all at once or one here and one there controlled by a local human-in-the-loop operator located at the front of the reusable part.