I've never used Azo or Amidol but when faced with a flat negative that needs more contrast than I can get with the hardest paper grade available I resort to underexposure and overdevelopment just as I would do when looking to increase the contrast when developing film.

The procedure is as follows. Make the best possible print even though you know it needs more contrast. Make a second print but reduce the exposure by 30 to 50% and process in the same developer used for the first print. You will have to develop by inspection which could take up to 40 minutes, that's the longest I've developed in these circumstances. I process in the dark, switching on the safelight occasionally to check the progress. Clearly there is a large degree of trial and error involved but it does work with both graded and VC papers. Don't be afraid to go to the extremes to get a result.