If I knew a program tailored to people like me that would give me a reasonably-accredited certificate and teach me the math and theory, I'd pay perhaps $20k for it. I'd go back to college, but I really don't want the pain of all that undergrad coursework.
As far as demonstrating it to employers, that comes down to the interviewing process, which is in and of itself pretty broken, but they'll probably just ask you a lot of contrived questions about that stuff.
Bonus: if one of them gets popular you'll have companies coming to you.
You're better off working through a problem set like Project Euler, or trying some TopCoder Single Round Matches (SRMs, there's a huge archive). At least that way you'll see some interesting puzzles and you'll get exposed to the majority of the 'standard' algorithms.
By the time you get 'good' you should be able to read a problem statement and immediately think "Ok, this is some kind of graph problem" or "List of sorted stuff? Probably need to use binary search". There are some good books like Skienna's the Algorithm Design Manual which encourages this kind of intuition.
Try to work on projects involving encoding/decoding video streams and displaying them on the screen.
Also, 3D game engines.