I'm wondering whether your H's self deprecating reponse might be his male version of an insecure woman's self deprecating remarks if a man gives her a compliment, or if a man makes a pass at her and she keeps saying no when she really means yes. If he responds as you say, then I read it as more a sign of his discomfort in being admired than not wanting you to say it.
In fact, he probably wants you to say it more but is too scared to admit to it. If he is not copnfident in his masculinity then I can see him thinking that asking for validation is being "wimpy." (BTW did he ever get teased about this sort of things from other boys when he was a kid?)
I am seeing your role as a mother trying to groom her son behind the scene to be confident, assertive, etc. That means there are times when the mom might have to smack her son to stand up straight and stick out his chest, but he knows she does it out of love for him. The military seems to have the same effect on some lost boys too. That's not going to be attractive to you, but that's what you have to work with.
