Very cool to see someone playing with my approach. Haven't checked your paper throughly, but the principle of packing 2 signatures in one is very useful. I was recently thinking about packing 1000s of signatures in one to help with crowdfunding and possibly a majority vote. Maybe it's possible with some more algebraic mumbo-jumbo.
I think my method is OK but there may be some attack I haven't considered.
It's very similar to your approach but for my method I had to add a step to stop someone cheating by declaring a false value for A.
I think it's interesting using the EC maths rather than the bicoin scripting for this type of thing - less problem with wallet compatibility and it works with most alt-currencies too.
The multiple signatures and crowd funding ideas are interesting. I was going to see if I could adapt it to a 2 of 3 signature when I get time.I think this type of thing could be useful in other distributed systems.