Good Bad Gerber, http://www.bridgematters.com/etmgbg.pdf, has an advanced section with this new response structure:

4D: Good, 0 to 2 aces
-- now 4H, 4S, 4NT, 5D asks partner to pass if 0, or show aces in steps
-- 5C asks for aces in steps
4H: Bad, 0 or 3 aces
4S: Bad, 1 or 4 aces
4NT: Bad, 2 aces
5C: Good, 3 aces
5D: Good, 4 aces

The response compression gives the partnership an excellent chance of staying low if partner has a bad hand and/or not enough aces. See the document for examples.